Fix test_mkpath_exception_uncached

[Avasam]

Attempt (because Ruff failures right now make this hard to confirm in isolation) at fixing the following test failure https://github.com/pypa/distutils/actions/runs/11999395994/job/33447255455?pr=314#step:5:187

__________________ TestDirUtil.test_mkpath_exception_uncached __________________

self = <distutils.tests.test_dir_util.TestDirUtil object at 0x7f66ff36a490>
monkeypatch = <_pytest.monkeypatch.MonkeyPatch object at 0x7f66ff180850>
tmp_path = PosixPath('/tmp/pytest-of-runner/pytest-0/test_mkpath_exception_uncached0')

    def test_mkpath_exception_uncached(self, monkeypatch, tmp_path):
        """
        Caching should not remember failed attempts.
    
        pypa/distutils#304
        """
    
        class FailPath(pathlib.Path):
            def mkdir(self, *args, **kwargs):
                raise OSError("Failed to create directory")
    
        target = tmp_path / 'foodir'
    
        with pytest.raises(errors.DistutilsFileError):
>           mkpath(FailPath(target))

distutils/tests/test_dir_util.py:130: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
/opt/hostedtoolcache/Python/3.11.10/x64/lib/python3.11/pathlib.py:871: in __new__
    self = cls._from_parts(args)
/opt/hostedtoolcache/Python/3.11.10/x64/lib/python3.11/pathlib.py:509: in _from_parts
    drv, root, parts = self._parse_args(args)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

cls = <class 'distutils.tests.test_dir_util.TestDirUtil.test_mkpath_exception_uncached.<locals>.FailPath'>
args = (PosixPath('/tmp/pytest-of-runner/pytest-0/test_mkpath_exception_uncached0/foodir'),)

    @classmethod
    def _parse_args(cls, args):
        # This is useful when you don't want to create an instance, just
        # canonicalize some constructor arguments.
        parts = []
        for a in args:
            if isinstance(a, PurePath):
                parts += a._parts
            else:
                a = os.fspath(a)
                if isinstance(a, str):
                    # Force-cast str subclasses to str (issue #21127)
                    parts.append(str(a))
                else:
                    raise TypeError(
                        "argument should be a str object or an os.PathLike "
                        "object returning str, not %r"
                        % type(a))
>       return cls._flavour.parse_parts(parts)
E       AttributeError: type object 'FailPath' has no attribute '_flavour'

The issue is that when instanciated, a Path checks whether it's an exact instance of Path before deferring its self/cls to WindowsPath or PosixPath, which do implement the _flavor attribute. But since FailPath is a subclass of Path, the overriding of cls never happens.