fixup! review

The `Python package` Windows jobs fail in
`test_root_update_skips_old_url_resolution_when_remote_matches[False]`
with `AssertionError: Previous URL does not need resolving`. The fixture
writes `source.working_tree_dir` with native backslashes into `.gitmodules`,
while `git clone` stores the submodule remote URL with forward slashes.
The test therefore requests a remote change instead of exercising the
intended existing-remote shortcut.

Pass the fixture's new URL through `Git.polish_url`, matching the stored
remote on Windows as well as POSIX. The production URL resolver and
remote-change behavior do not need changing.

Validation: both targeted dry-run cases pass. An assert-based local
reproduction using backslash paths fails before this change and passes
afterwards. The relative URL tests pass (32 passed, 2 platform skips),
the offline submodule update tests pass (68 passed), and Ruff lint,
formatting, and `git diff --check` pass. Local test commits use a
command-scoped `commit.gpgSign=false` setting. Native Windows validation
is delegated to the PR CI jobs.

Author: codex

test/test_submodule.py

@@ -103,7 +103,7 @@ def test_root_update_skips_old_url_resolution_when_remote_matches(tmp_path, dry_
             writer.set_value("url", "../source")
         previous = parent.index.commit("Record relative submodule URL")
         with submodule.config_writer() as writer:
-            writer.set_value("url", source.working_tree_dir)
+            writer.set_value("url", Git.polish_url(source.working_tree_dir))
         parent.index.commit("Use existing remote URL")
 
         resolve_url = Submodule._resolved_url