Errors in testing exit codes

As seen in #606, there are errors along the lines of

```
>       assert result.exit_code == 2
E       AssertionError: assert 1 == 2
E        +  where 1 = <Result ValueError('A calculator must be attached to `struct`')>.exit_code

tests/test_singlepoint_cli.py:574: AssertionError
```

This is happening on `main` too, and probably from click 8.3.0, released yesterday.