This fixes a problem where each workflow would get their own merge
commit. This happens frequently when the target branch is merged into a
the same time, different workflows in the same run will run
get-merge-commit at different times and thus have different merge
commits.
Since the jobs don't really depend on each other, this doesn't cause
practical problems, yet. But it has already led to strange CI failures
in a still unmerged PR, which can be prevented from happening with this
clean approach.
And yes, this saves a few API calls on every run.
09ddb1a8a0