plugin rapidly drains GitHub API quota in poll mode

We recently upgraded to 1.32.8 (from 1.31.4, since many intervening versions have been broken in different ways), and we’re quickly burning through all of our GitHub API quota:

$ while true; do curl -slL https://api.github.com/rate_limit?access_token=[elided] | jq .resources.core.remaining ; sleep 1; done
592
591
589
587
586
584
582
575
564
553
545
535
529
519
509
500
491
483
478
476
473

Note that I restarted the plugin about 15m ago; this ratelimit value starts at 5000.

Looking at the Jenkins log, it looks like its querying each PR multiple times per minute. Refreshing the log, I’ll see things like

Jul 05, 2016 10:05:04 PM INFO org.jenkinsci.plugins.ghprb.GhprbPullRequest updatePR
Pull request #16,062 was updated on repo kubernetes/kubernetes but there aren't any new comments nor commits; that may mean that commit status was updated.
Jul 05, 2016 10:05:04 PM INFO org.jenkinsci.plugins.ghprb.GhprbPullRequest updatePR
Pull request #13,925 was updated on repo kubernetes/kubernetes but there aren't any new comments nor commits; that may mean that commit status was updated.
Jul 05, 2016 10:05:04 PM INFO org.jenkinsci.plugins.ghprb.GhprbPullRequest updatePR
Pull request #13,216 was updated on repo kubernetes/kubernetes but there aren't any new comments nor commits; that may mean that commit status was updated.

repeated again and again for the same PRs, even though nothing is changing.

[unphased]

Sad to see this six year old issue is still pending without any workaround or resolution. Might need to go ahead and try the webhook relay.

[RoyTinker]

Filed a separate issue for adding If-Modified-Since to request headers when polling PRs: #653