Let pathlib resolve the flavor.

Author: jaraco

distutils/tests/test_dir_util.py

@@ -126,11 +126,7 @@ def mkdir(self, *args, **kwargs):
                 raise OSError("Failed to create directory")
 
             if sys.version_info < (3, 12):
-                _flavour = (
-                    pathlib._windows_flavour
-                    if os.name == 'nt'
-                    else pathlib._posix_flavour
-                )
+                _flavour = pathlib.Path()._flavour
 
         target = tmp_path / 'foodir'