Pin specific runner image versions.

[desrosj]

While it would be nice to always use *-latest images, it's proven to be problematic enough to consider pinning specific versions of runner images.

• Because images are deployed over week long (sometimes month long) periods, it's not uncommon for workflows to have warning notices that GH adds for awareness that do not have any impact on the workflow's result. This makes it hard to separate legitimate failures/problems from these warnings.
• As images slowly roll out, things can suddenly start to fail. See Core-62843 and Core-62808 as examples.

Trac ticket: https://core.trac.wordpress.org/ticket/62221

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Props desrosj.

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[github-actions]

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[johnbillion]

Fully agreed

[desrosj]

Merged in https://core.trac.wordpress.org/changeset/59720.