Add testing for new MySQL "Innovation" releases

[desrosj]

Trac ticket: https://core.trac.wordpress.org/ticket/59779

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[johnbillion]

We're at 500 GHA jobs with this configuration. Is that the limit?

[desrosj]

Concurrently, yes. But this includes the Upgrade and Installation tests, which do not run on PRs or commits unless the corresponding workflow file is modified (or run manually). The installation test workflow accounts for 72 jobs, and the upgrade testing one has 384 in this run (some are not counted because the matrix was too large).

So for normal pushes and PRs, we're sitting around around 150-200.

It looks like the matrices in the upgrade testing workflow puts several of the jobs over the maximum allowed number of 255. I think I'll proceed with testing against these innovation releases in the PHPUnit workflow only for now.

[desrosj]

Merged in https://core.trac.wordpress.org/changeset/57132. We can revisit the upgrade/install testing at a later time.