Improved error message from: [directory] is not a valid Python package name #17108

Bug Report

Executing mypy fails with some strange error message.

To Reproduce

>>> mypy run cognite/neat
source-graphs is not a valid Python package name

In the root of the public repo: https://github.com/cognitedata/neat

Same for dmypy

>>> dmypy run -- cognite/neat
source-graphs is not a valid Python package name

Expected Behavior

Execute validation of the files in the package.

Actual Behavior

It responds: source-graphs is not a valid Python package name

Digging into the source code of mypy it seems to be hitting here
https://github.com/python/mypy/blob/master/mypy/find_sources.py#L187

Your Environment

• Mypy version used: 1.9
• Mypy command-line flags:
• Mypy configuration options from mypy.ini (and other config files):

[tool.mypy]
explicit_package_bases = true
allow_redefinition = true
plugins = ["pydantic.mypy"]

• Python version used: 3.12
• OS: Windows

If I specify a different path MyPy works as normal, for example,

mypy run cognite/neat/rules