Upgrade gitlab-styles to 6.1.0

What does this MR do?

This MR upgrades to gitlab-styles 6.1.0.

It adds a new 👮 Style/HashTransformation (added via https://gitlab.com/gitlab-org/gitlab-styles/-/merge_requests/72 and tracked in #322739 (closed)) and enables a couple of vendor 👮 (see .rubocop_todo.yml).

📣 Please announce in #backend when merged and promote the follow-up #322739 (closed).

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content