CI optimization: running only affected tests per PR

[Ken Isiaho (leader-ke)]

Hi — I was looking at open-source projects with long CI times and noticed your test runs average 35 minutes (up to 51 min recently).

One approach that's worked well for projects I maintain: running only the tests affected by each PR's changed files instead of the full suite. For reference, here's an open-source GitHub Action that does this: pemystack/greenlight-action.

Not pushing anything — just flagging since long CI is one of the top contributors to slow PR review cycles. Happy to share more details on the approach if it's useful.

[Wessel (wesselb)]

Hey Ken Isiaho (@leader-ke)! Thanks for raising the idea. This could be a useful improvement in the future. Currently, I don't think CI wait times are blocking and I'd prefer to run all files every time, so we are sure all regressions are caught.