Improvements to tracked background migration tests

What does this MR do and why?

Update edit: MR wasn't merged, DB team to own followup: !83164 (comment 885855843)

This change adds explicit tests to all background migrations that pass track_jobs: true

The testing also revealed a number of migrations that would leave a job forever in pending mode because it wasn't marking the job as successful in every possible situation (including scenarios on EE instances where the data targeted does not exist, or on CE instances where the migration should not have run)

These changes are primarily with self-managed instances in mind and are an attempt at lowering the support team's burden from customers observing jobs permanently stuck in pending despite its work being complete. This MR is similar in goal to !81879 (merged) but now attempts to cover all of the currently existing background migrations

Screenshots or screen recordings

N/A

How to set up and validate locally

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MR acceptance checklist

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