tests: Fix path issue on annoying operating system

Author: pawamoy

tests/test_handler.py

@@ -141,7 +141,8 @@ def test_extension_paths(tmp_path: Path, expect_change: bool, extension: str | d
             assert normalized == str(tmp_path.joinpath(extension))
         elif isinstance(normalized, dict) and isinstance(extension, dict):
             pth, options = next(iter(extension.items()))
-            assert normalized == {str(tmp_path.joinpath(pth)): options}
+            #
+            assert normalized == {str(Path(tmp_path, pth)): options}
         else:
             raise ValueError("Normalization must not change extension items type")
     else: