What we need is a way to tell GitLab "queue `build-only` jobs after
`build-for-tests` jobs have started", to make sure that `build-only`
jobs don't start before `build-for-tests` jobs and thus delays test jobs
and the overall pipeline.
The best I had found was "queue `build-only` jobs after *all* the
`build-for-tests` jobs have finished", but this introduces a larger
delay than we want, and causes `build-only` jobs to often be the last
ones to finish in a pipeline, after test jobs that respect the 15min
runtime limit.
Instead, we can tell GitLab "queue `build-only` jobs after the
`build-for-tests` jobs have been queued for X minutes", which is closer
to what we want, and in particular this ensures the correct order of
*starting* jobs as long as the CI is not overwhelmed and doesn't manage
to actually start a queued `build-for-tests` job within 5min, in which
case I'd argue we don't care about job order anymore because we have
bigger problems anyway and likely everything's going to timeout.
This also gets rid of the hard-to-maintain `.build-for-tests-jobs` list
of `needs:`, which also needed to be manually merged in half the jobs.
The trade-off is that we need to make a (shallow) copy of the
`.container+build-rules` list, that replaces all the `when: on_success`
with `when: delayed` + `start_in: 5 minutes`. This means that we'll need
to make sure the two lists of conditions remain identical, but this
seems more manageable; nevertheless, I added a comment to remind us.
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/33564>
a66e227748