NewNoteWorker jobs are backlogged

I've been noticing e-mails for new notes are being delayed quite a bit:

• https://performance.gitlab.net/dashboard/db/sidekiq-workers?orgId=1&var-worker=NewNoteWorker%23perform&var-database=Production

Timings are pretty bad:

• 

Likely related to https://gitlab.com/gitlab-org/gitlab-ce/issues/45534. This is similar to https://gitlab.com/gitlab-org/gitlab-ce/issues/45526.