Lefthook: Do not reveal RuboCop TODOs in pre-push hook

What does this MR do?

Having REVEAL_RUBOCOP_TODO=1 reveals RuboCop TODOs and sometimes prevents pushing code.

This commit hides any RuboCop TODOs in lefthook.

This came up during the review of !56827 (comment 531078988).

Reproduction

• export REVEAL_RUBOCOP_TODO=1
• Make an RuboCop rule unrelated change to a Ruby file which now contains revealed TODOs
• bundle exec lefthook run pre-push or git push

Screenshots (strongly suggested)

Before	After

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
  • [-] I have included a changelog entry.
  • I have not included a changelog entry because it's a developer-facing change.
• [-] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content