Use `workflow_run` trigger instead of `ArcticLampyrid/action-wait-for-workflow`

[make-github-pseudonymous-again]

See https://docs.github.com/en/actions/using-workflows/events-that-trigger-workflows#workflow_run. We could even read artifacts produced by the triggering workflow, see https://docs.github.com/en/actions/using-workflows/events-that-trigger-workflows#using-data-from-the-triggering-workflow. One draw-back is that we will not be able to test this works in a PR because workflow_run-triggered workflows only run when they exist on the default branch.

[make-github-pseudonymous-again]

We could also consider not waiting at all and instead use the cache from previous run. Or we could wait a limited amount of time, but fallback to caches from previous run if we reach the timeout instead of failing.