See INFRA-1633 for a real use-case on ci.jenkins.io. Some pull requests are stale OR contain no content to rebuild, and it does not make sense to run CI against them and to consume resources each time builds are retriggered.
I suggest adding a new trait which allows skipping pull requests if they are labeled by "skip-ci" or such labels
I wrote a plugin to do this for myself a long time ago, never got to publishing it because I couldn't hook up an event subscriber thing for github pull request label events. My use case was for opting-in pull requets based on label but I think I wrote the excluding case as well. I can throw what I have on github tomorrow.