Github actions for watching PRs merged into a given branch (e.g., 'beta'). When a PR is merged it's labeled with the given merged-label-name,
helping to keep track of PRs that are in beta for example. If a push occurs into the PR's branch and it was already labeled with the merged-label-name, it will label the PR now with the stale-merged-label-name, meaning that the PR was merged into, for example,
beta, but now an older version is merged there.