Support venv detection on Windows with mingw Python

[zachsnicker]

closes #12544

• Updated the _in_venv function in src/_pytest/main.py to correctly detect Python virtual environments.
• Updated the test cases in testing/test_collection.py to validate the new behavior.
• Created a changelog fragment to document this improvement.

[lazka]

These docs need to be updated too: https://github.com/pytest-dev/pytest/blob/main/doc/en/reference/reference.rst?plain=1#L1705-L1706

I'd guess just removing the " by the presence of an activation script" should be enough. The users shouldn't need to care how it's done.

Otherwise lgtm, code wise.

[bluetech]

Thanks @zachsnicker, and @lazka for the review.

[webknjaz]

I edited this entry a little, in #12559. Preview: https://pytest--12559.org.readthedocs.build/en/12559/changelog.html#improvements-in-existing-functionality.

[jezdez]

Seems like this is basically breaking pytest support in conda environments, can we revert this change until we've reliably roll out pyvenv.cfg in conda envs (see recent conversations in conda/conda#13337)?

[RonnyPfannschmidt]

@jezdez is there a good way to check for conda prior to that change? im happy to roll back for now, but if a consistent bugfix that ensures compatibility with older conda is easy, i'd prefer landing that over a revert dance

[jezdez]

@jezdez is there a good way to check for conda prior to that change? im happy to roll back for now, but if a consistent bugfix that ensures compatibility with older conda is easy, i'd prefer landing that over a revert dance

Actually, apologies for responding to a closed PR, can we move that into #12652 please?