Handle undecodable repository metadata on Windows

Python 3.9 on Windows raised UnicodeDecodeError while the repository-discovery regression test parsed invalid commondir bytes, causing the Python package test (windows, 3.9) check to fail.

Treat UnicodeError like an unreadable metadata file in both commondir and gitfile parsing. Invalid bytes now make discovery reject the candidate repository, matching Git's behavior.

Validation: env PYTHONPATH=gitdb:smmap .venv/bin/python -m pytest -q test/test_repo.py::TestRepo::test_repo_discovery_rejects_invalid_metadata; .venv/bin/python -m compileall -q git/repo/fun.py; git diff --check

Author: codex

git/repo/fun.py

@@ -94,7 +94,7 @@ def is_git_dir(d: PathLike) -> bool:
                 if osp.lexists(common_dir_file):
                     return False
                 common_dir = os.fspath(d)
-            except OSError:
+            except (OSError, UnicodeError):
                 return False
             else:
                 if not common_dir:
@@ -125,7 +125,7 @@ def find_worktree_git_dir(dotgit: PathLike) -> Optional[str]:
 
     try:
         content = os.fsdecode(Path(dotgit).read_bytes()).rstrip("\r\n")
-    except OSError:
+    except (OSError, UnicodeError):
         return None
     return content[8:] if len(content) >= 9 and content.startswith("gitdir: ") else None