Update the value of AllCops.MaxFilesInCache in .rubocop.yml

The following discussion from !96106 (merged) should be addressed:

• @godfat-gitlab started a discussion: (+10 comments)

  This test is added in !70497 (merged) and I am not fully clear about the context. /cc @rymai @splattael

  This is documented at: https://docs.rubocop.org/rubocop/usage/caching.html#cache-pruning

  I think this is fine as a quick fix for JiHu, however we should find a better approach in the future.

  @rymai Could you please review this? This is considered a high priority because of JiHu Broken Pipeline. Thank you!.