Trim the 6.5 workflows

[johnbillion]

Previously: #10165

The reusable workflow files have already been removed from this branch.

Trac ticket: https://core.trac.wordpress.org/ticket/64083

[github-actions]

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Props johnbillion.

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[github-actions]

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[desrosj]

Just one question, but looks good.

[desrosj]

Same question here as in #11043 about 10.4/10.6. Won't leave this on #11405, etc., but it looks like same comment there.