COVERAGE_CORE=sysmon now produces an error for python3.12

**Describe the bug**

With v7.11.1 of coverage-py and python3.12, what was previously a warning is now an exception. I was surprised to see this happen on a bugfix, rather than a breaking change. I'm mostly reporting this for other users that might be having a similar issue.

We use `COVERAGE_CORE=sysmon` to account for a performance issue between python versions. This produced a warning that we were able to suppress, as we were fine with ignoring for older versions of python. Now with v7.11.1 this is an exception we can't ignore. See: https://github.com/nedbat/coveragepy/issues/1812#issuecomment-2576969445 for similar comments to ours.


Before:
```
/usr/local/lib/python3.12/site-packages/coverage/core.py:81: CoverageWarning: sys.monitoring can't measure branches in this version, using default core (no-sysmon); see https://coverage.readthedocs.io/en/7.11.0/messages.html#warning-no-sysmon
  warn(f"sys.monitoring {reason_no_sysmon}, using default core", slug="no-sysmon")
```

Now:
```
  File "/usr/local/lib/python3.12/site-packages/coverage/core.py", line 94, in __init__
    raise ConfigError(
coverage.exceptions.ConfigError: Can't use core=sysmon: sys.monitoring can't measure branches in this version
```

**To Reproduce**

Make a project with `python_version = '==3.12'`, `coverage==7.11.1`, `pytest`, and `pytest-cov`. Then run pytest. I've put a script below to make a small example.

```sh
#!/bin/bash

# Create directory structure
mkdir -p "testpackage/src/testpackage"
mkdir -p "testpackage/tests"

# Create pyproject.toml
cat > "testpackage/pyproject.toml" << 'EOF'
[project]
name = "testpackage"
version = "0.1.0"
description = "Add your description here"
requires-python = "==3.12"
dependencies = [
    "pytest==8.4.2",
    "coverage==7.11.0",
    "pytest-cov==7.0.0",
]

[build-system]
requires = ["uv_build>=0.9.7,<0.10.0"]
build-backend = "uv_build"

[tool.pytest.ini_options]
testpaths = ["tests"]
addopts = [
    "--cov=testpackage",
    "--cov-report=html",
    "--cov-report=term-missing",
]

[tool.coverage.run]
source = ["src"]
branch = true
core = "sysmon"

EOF

# Create src/testpackage/__init__.py
cat > "testpackage/src/testpackage/__init__.py" << 'EOF'
def main() -> None:
    print("Hello from testpackage!")

def add_numbers(a, b):
    """Simple function to add two numbers."""
    return a + b
EOF

# Create tests/test_example.py
cat > "testpackage/tests/test_example.py" << 'EOF'
"""
Example pytest test file demonstrating basic testing patterns.
"""
import pytest
from testpackage import add_numbers


def test_add_positive_numbers():
    """Test adding positive numbers."""
    result = add_numbers(2, 3)
    assert result == 5
EOF

cd testpackage

uv run pytest # <-- observe no error
uv add coverage==7.11.1
uv run pytest # <-- observe error

```

The first run outputs:

```
================================================================================== test session starts ===================================================================================
platform linux -- Python 3.12.0, pytest-8.4.2, pluggy-1.6.0
rootdir: /tmp/testpackage
configfile: pyproject.toml
testpaths: tests
plugins: cov-7.0.0
collected 1 item                                                                                                                                                                         

tests/test_example.py .                                                                                                                                                            [100%]

==================================================================================== warnings summary ====================================================================================
```

The second test outputs

```
Traceback (most recent call last):
  File "/tmp/testpackage/.venv/bin/pytest", line 10, in <module>
    sys.exit(console_main())
             ^^^^^^^^^^^^^^
  File "/tmp/testpackage/.venv/lib/python3.12/site-packages/_pytest/config/__init__.py", line 201, in console_main
    code = main()
           ^^^^^^
  File "/tmp/testpackage/.venv/lib/python3.12/site-packages/_pytest/config/__init__.py", line 156, in main
    config = _prepareconfig(args, plugins)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/tmp/testpackage/.venv/lib/python3.12/site-packages/_pytest/config/__init__.py", line 342, in _prepareconfig
    config = pluginmanager.hook.pytest_cmdline_parse(
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/tmp/testpackage/.venv/lib/python3.12/site-packages/pluggy/_hooks.py", line 512, in __call__
    return self._hookexec(self.name, self._hookimpls.copy(), kwargs, firstresult)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/tmp/testpackage/.venv/lib/python3.12/site-packages/pluggy/_manager.py", line 120, in _hookexec
    return self._inner_hookexec(hook_name, methods, kwargs, firstresult)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/tmp/testpackage/.venv/lib/python3.12/site-packages/pluggy/_callers.py", line 167, in _multicall
    raise exception
  File "/tmp/testpackage/.venv/lib/python3.12/site-packages/pluggy/_callers.py", line 139, in _multicall
    teardown.throw(exception)
  File "/tmp/testpackage/.venv/lib/python3.12/site-packages/_pytest/helpconfig.py", line 112, in pytest_cmdline_parse
    config = yield
             ^^^^^
  File "/tmp/testpackage/.venv/lib/python3.12/site-packages/pluggy/_callers.py", line 121, in _multicall
    res = hook_impl.function(*args)
          ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/tmp/testpackage/.venv/lib/python3.12/site-packages/_pytest/config/__init__.py", line 1146, in pytest_cmdline_parse
    self.parse(args)
  File "/tmp/testpackage/.venv/lib/python3.12/site-packages/_pytest/config/__init__.py", line 1527, in parse
    self._preparse(args, addopts=addopts)
  File "/tmp/testpackage/.venv/lib/python3.12/site-packages/_pytest/config/__init__.py", line 1431, in _preparse
    self.hook.pytest_load_initial_conftests(
  File "/tmp/testpackage/.venv/lib/python3.12/site-packages/pluggy/_hooks.py", line 512, in __call__
    return self._hookexec(self.name, self._hookimpls.copy(), kwargs, firstresult)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/tmp/testpackage/.venv/lib/python3.12/site-packages/pluggy/_manager.py", line 120, in _hookexec
    return self._inner_hookexec(hook_name, methods, kwargs, firstresult)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/tmp/testpackage/.venv/lib/python3.12/site-packages/pluggy/_callers.py", line 167, in _multicall
    raise exception
  File "/tmp/testpackage/.venv/lib/python3.12/site-packages/pluggy/_callers.py", line 139, in _multicall
    teardown.throw(exception)
  File "/tmp/testpackage/.venv/lib/python3.12/site-packages/_pytest/warnings.py", line 129, in pytest_load_initial_conftests
    return (yield)
            ^^^^^
  File "/tmp/testpackage/.venv/lib/python3.12/site-packages/pluggy/_callers.py", line 139, in _multicall
    teardown.throw(exception)
  File "/tmp/testpackage/.venv/lib/python3.12/site-packages/_pytest/capture.py", line 173, in pytest_load_initial_conftests
    yield
  File "/tmp/testpackage/.venv/lib/python3.12/site-packages/pluggy/_callers.py", line 121, in _multicall
    res = hook_impl.function(*args)
          ^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/tmp/testpackage/.venv/lib/python3.12/site-packages/pytest_cov/plugin.py", line 200, in pytest_load_initial_conftests
    plugin = CovPlugin(options, early_config.pluginmanager)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/tmp/testpackage/.venv/lib/python3.12/site-packages/pytest_cov/plugin.py", line 250, in __init__
    self.start(engine.Central)
  File "/tmp/testpackage/.venv/lib/python3.12/site-packages/pytest_cov/plugin.py", line 263, in start
    self.cov_controller.start()
  File "/tmp/testpackage/.venv/lib/python3.12/site-packages/pytest_cov/engine.py", line 55, in ensure_topdir_wrapper
    return meth(self, *args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/tmp/testpackage/.venv/lib/python3.12/site-packages/pytest_cov/engine.py", line 284, in start
    self.cov.start()
  File "/tmp/testpackage/.venv/lib/python3.12/site-packages/coverage/control.py", line 694, in start
    self._init_for_start()
  File "/tmp/testpackage/.venv/lib/python3.12/site-packages/coverage/control.py", line 586, in _init_for_start
    self._core = Core(
                 ^^^^^
  File "/tmp/testpackage/.venv/lib/python3.12/site-packages/coverage/core.py", line 94, in __init__
    raise ConfigError(
coverage.exceptions.ConfigError: Can't use core=sysmon: sys.monitoring can't measure branches in this version
```

**Expected behavior**

**Warning to occur and to fallback to `core`**




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COVERAGE_CORE=sysmon now produces an error for python3.12 #2076

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COVERAGE_CORE=sysmon now produces an error for python3.12 #2076

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