For unknown reasons, this is now necessary

Otherwise, the sub-projects have both hostlabels as constraints. Was not
enforced like this before 2021-10-29. But now something triggered this,
possibly it was always ment to be like this? Only thing that happened
today was an OOM initiated kill of bs_sched on obs-backend, that maybe
re-read information that was stale for a long time.

Oh well...
2 jobs for master in 9 seconds (queued for 9 seconds)