Cache rubocop cache for CI

What does this MR do?

Cache rubocop cache for CI

Are there points in the code the reviewer needs to double check?

It's not always reducing the time. I wish we could peek at the cache to verify if the cache is there or not.

Why was this MR needed?

Speed up rubocop check.

Does this MR meet the acceptance criteria?

• Tests added for this feature/bug
• Review
  • Has been reviewed by Backend

What are the relevant issue numbers?

Closes #42338 (closed)

@rspeicher Please review, thanks!