docs only changes PRs can't be merged because of `set_status` job requirement

[NeroBurner]

When a PR touches only the docs folder the resulting PRs can't get a green status. The set_status job is required, but will never be run

The status for maintainer will look like this, never enabling the merge button

[NeroBurner]

found the following explanation https://stackoverflow.com/questions/52200096/github-pull-request-waiting-for-status-to-be-reported

It doesn't perfectly fit our case (the issue is about sometimes hanging PRs), but maybe it is useful information on our path to find a fix