Fix exclusive lease usage in transaction for app/mailers/previews/notify_preview.rb

See original issue in #440368 (closed)

Problem: The cleanup method wraps the email-generating-block in a transaction. See https://gitlab.com/gitlab-org/gitlab/-/blob/ea71b210ca72ab6a061ffb3df09ed03b50e231c8/app/mailers/previews/notify_preview.rb#L247 for example.

Progress

The notify_preview.rb file contains multiple leases to be fixed, owned by different groups.

• grouprespond - All service_Desk related leases have been fixed with !150706 (merged)
• groupcode review - note_email needs to be fixed, by investigating enqueue_diff_file_creation_job in app/models/diff_note.rb, see: !150706 (diffs). Update: does not need to be fixed, see !155252 (merged)