Quick fix to identify git repo, worktree or submodule (#249)

Co-authored-by: Sam Clarke-Green <74185251+t00sa@users.noreply.github.com>

Author: yaswant

script_umdp3_checker/umdp3_conformance.py

@@ -489,7 +489,8 @@ def print_in_box_b(
 def which_cms_is_it(path: str, print_volume: int = 3) -> CMSSystem:
     """Determine which CMS is in use based on the presence of certain files."""
     repo_path = Path(path)
-    if (repo_path / ".git").is_dir():
+    if (repo_path / ".git").exists():
+        # valid for a repo, worktree, or submodule
         cms = GitBdiffWrapper(repo_path)
     elif (repo_path / ".svn").is_dir():
         """