Fix excluded files for RSpec/EmptyLineAfterFinalLetItBe cop

Why are we doing this work

We have recently introduced a new cop called RSpec/EmptyLineAfterFinalLetItBe and some of the files are excluded as they are currently not confirming with this new cop. We should fix those files and remove the entire exclude list for this new cop from the .rubocop_manual_todo.yml file.

Relevant links

• The MR which introduced this cop: https://gitlab.com/gitlab-org/gitlab-styles/-/merge_requests/80
• The MR which enabled the cop and excluded the files: !57361 (merged)

Implementation plan

The cop already provides an auto-fix but the output should be manually checked and the list is huge.

• backend Remove the exclude list for RSpec/EmptyLineAfterFinalLetItBe and then run rubocop --only RSpec/EmptyLineAfterFinalLetItBe -a to fix the failures