When hitting a treewide, we would previously find the username for each
user and then check all of them for collaborator status - only to then
realize that this results in more than 15 reviewers and exit.
We can put a simple stop-gap in, even before de-duplicating the combined
lists of maintainers and owners as safe guard. We could still hit huge
numbers of code owners, but in practice we don't nearly as many as
maintainers, so this will be sufficient for now.
The recent change to use the result of requesting reviewers for setting
the `needs: reviewer` label caused a regression: It would not set the
label for PRs where no reviewers were requested, because *too many were
eligible*. Still - these PRs don't have reviewers, so they need
attention otherwise - via the label.
This was introduced shortly before merge of the reviewers.js file, but
not actually tested - I thought it was not easy to find a PR triggering
this warning. However, the scheduled run told me otherwise: The
staging-next PR is the perfect candidate.
This migrates the bash code to request reviewers to github-script. This
will allow multiple nice improvements later on, but at this stage it's
mostly a reduction in code and complexity.