Describe the bug
Consider this backport:

It had been merged by Mergify but you can see that CI hadn't finished (the gold dot by the title). This is a big problem. It hits backports especially hard because they don't have the 2-days delay that we have on master.

Any PR that has all the necessary labels and approvals will be merged once all the required jobs are finished. But what are "required" jobs? Take validate-post: it can be done by either the validate.yml workflow or validate-skip.yml. Unfortunately, Mergify is unable to tell when it should wait for the former and when the latter suffices. The original idea was that for documentation changes the latter should do it. But the way this was implemented in #9355 confuses Mergify. Granted, this roundabout way of supporting documentation-only changes is the only way for all GitHub users. But not all GitHub users use Mergify, so they're mostly fine with this -skip hack. We are not because, again, Mergify doesn't understand the distinction and is happy to merge whenever -skip workflows are done (besides validate-skip.yml we have a bunch of other *-skip workflows).

How to fix

I propose we rip out the -skip workflows for now and go back to the drawing board.