Add test for Pytest issue 9765

[lesteve]

pytest-dev#9765

For some reason, the error in the test is not exactly the same assert mod not in mods as in the reproducer https://github.com/lesteve/pytest-issue-9765-reproducer but this seems close enough, note the capital C: vs small c: in the paths:

ImportError while loading conftest 'C:\msys64\tmp\pytest-of-rjxQE\pytest-32\test_issue_97650\my_package\conftest.py'.
_pytest.pathlib.ImportPathMismatchError: ('my_package.conftest', 'c:\\msys64\\tmp\\pytest-of-rjxqe\\pytest-22\\test_i
ssue_97650\\my_package\\conftest.py', WindowsPath('C:/msys64/tmp/pytest-of-rjxQE/pytest-32/test_issue_97650/my_packag
e/conftest.py'))