Fix: Rebuild python-scripts image with updated cache cleanup script

Summary

The buildkit_cache_cleanup job was failing with:

TypeError: string indices must be integers, not 'str'

The fix for this was already committed in de4ac49 (Dec 28), but the python-scripts:latest Docker image was never rebuilt because subsequent commits didn't touch scripts/python/.

This MR triggers a rebuild of the image by fixing a minor typo in the docstring.

Root Cause

The GitLab container registry API returned unexpected data (string instead of list of dicts) for repository 634's tag list. The updated script has defensive type checking to handle this gracefully.