Apply suggestions from code review

Co-authored-by: Ernst Würger <[email protected]>

open_api_client_build/build_client.py

@@ -20,7 +20,7 @@
 error_code_pattern = re.compile("[4,5][0-9]{2}")
 
 
-def fix_spec(src, path):
+def fix_spec(src: str, path: str | os.PathLike):
     """Fix errors in the specification."""
     if src == "path":
         with open(path, "r") as f: