Fix: Update sync function to accept optional config parameter

Make config parameter in sync function explicitly optional in type signature to match actual behavior. This improves type checking without changing functionality.

Author: tony

src/vcspull/cli/sync.py

@@ -66,7 +66,7 @@ def create_sync_subparser(parser: argparse.ArgumentParser) -> argparse.ArgumentP
 
 def sync(
     repo_patterns: list[str],
-    config: pathlib.Path,
+    config: pathlib.Path | None,
     exit_on_error: bool,
     parser: argparse.ArgumentParser
     | None = None,  # optional so sync can be unit tested