Fix order dependent cleanup package file worker spec

What does this MR do and why?

This MR fixes an order dependent spec. It also fixes some RuboCop TODOs 💅

See #359097 (closed)

To quote: https://docs.gitlab.com/ee/development/testing_guide/best_practices.html#common-test-setup

As much as possible, do not implement this using before(:all) or before(:context). If you do, you would need to manually clean up the data as those hooks run outside a database transaction.

Screenshots or screen recordings

n/a

How to set up and validate locally

while :; do bin/rspec --order rand ./spec/workers/packages/cleanup_package_file_worker_spec.rb || break; done

MR acceptance checklist

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