add docstring

Author: lijinf2

ci/tools/check_pixi_cuda_version.py

@@ -17,6 +17,7 @@
 
 
 def main() -> int:
+    """Verify cuda_bindings/cuda_core pixi cu13 pins match ci/versions.yml."""
     if not VERSIONS_FILE_PATH.is_file():
         print(f"error: {VERSIONS_FILE_PATH} not found", file=sys.stderr)
         return 2