Skip the test if undecodable paths are not supported

The file system can reject a name with undecodable bytes even if
TESTFN_UNDECODABLE is not None (e.g. on macOS).

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: serhiy-storchaka

Lib/test/test_pydoc/test_pydoc.py

@@ -1032,7 +1032,10 @@ def test_html_doc_undecodable_path(self):
         with os_helper.temp_cwd() as test_dir:
             subdir = os.path.join(os.fsencode(test_dir),
                                   os_helper.TESTFN_UNDECODABLE)
-            os.mkdir(subdir)
+            try:
+                os.mkdir(subdir)
+            except OSError:
+                self.skipTest('undecodable paths are not supported')
             with open(os.path.join(subdir, b'undecodable_mod.py'), 'w') as f:
                 f.write('"""Module docstring."""\n')
             with import_helper.DirsOnSysPath(os.fsdecode(subdir)):