Revert migration squash that breaks 15.11

What does this MR do and why?

In April, I had !116021 (merged) merged, which squashed a migration that had a timestamp from January, but its corresponding commit was dated for October, which is after the squash date. This caused #409331 (closed), which prompted me to revert the squash in !118368 (merged). The revert was not present in 15.11.0 and 15.11.1, so any upgrades from 15.11.x to 16 will result in the un-squashed migrations being present for the upgrade, resulting in db:migrate attempting to re-run the init_schema migration, which naturally results in a failure.

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• This MR is backporting a bug fix, documentation update, or spec fix, previously merged in the default branch.
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