tests/sync(fix[update_repo]): Remove unused type: ignore comment

why: rev is typed str | None, so assigning None needs no suppression.
mypy flags the unused comment as an error.
what:
- Remove unused type: ignore[assignment] on git_repo.rev = None

Author: tony

tests/sync/test_git.py

@@ -1147,7 +1147,7 @@ def test_update_repo_symbolic_ref_failure_recorded(
     git_repo.run(["checkout", head_sha])
 
     # Ensure no rev is set so the code path hits symbolic_ref
-    git_repo.rev = None  # type: ignore[assignment]
+    git_repo.rev = None
 
     result = git_repo.update_repo()