Build bots are swamped with old PRs

[mcourteaux]

We should take out halidebuildbots as reviewer from old PRs. Everytime we commit to main, the bots are working for close to a day to process all PRs. All active PRs are needlessly stalled because we are "waiting for green" while the bots are compiling code from 2019.

[abadams]

The buildbots are rechecking PRs that haven't had a commit pushed to them? Can you point me to an instance? That shouldn't be happening.

[mcourteaux]

Here is one still going right now: https://buildbot.halide-lang.org/master/#/builders/67/builds/30, from #8207.

It seems that buildbots don't retry when there are merge conflicts in the files.

[mcourteaux]

To be honest, I think this is desirable behavior from the bots. You wouldn't want the bots to go green, then commit to main, have the PR silently break, and then we merge thinking all was good, but actually not.