CI: Use arm64 runners

[bquorning]

CI: Use arm64 runners

We can now run on the arm based CI runners: https://github.blog/changelog/2025-01-16-linux-arm64-hosted-runners-now-available-for-free-in-public-repositories-public-preview/

Our CI generally runs pretty fast, so it's hard to see any real difference in runtime yet. However, the two relatively slow JRuby jobs finished 10-15% faster on this PR than they did on the latest CI run on the master branch (master vs this PR).

Links:

• GitHub’s documentation of Standard GitHub-hosted runners for public repositories
• The Readme for the Ubuntu 22.04 by Arm Limited runner image.

[pirj]

Maybe we should just remove JRuby jobs?

I'd let GitHub choose what they want to run our CI on, if arm64 is more effective, we don't mind (if they even need us to agree).

[bquorning]

How do we let GitHub choose?

[pirj]

https://github.com/actions/runner-images/blob/af0df299674bc781d6a4f891d9cea62b438e1332/images/ubuntu/Ubuntu2404-Readme.md?plain=1#L8 doesn't explicitly tell it's an X86-64, except for a few (Java, Chromium) packages pointing to that. I don't see why GitHub wouldn't want to silently switch those for ARM runners sometimes in the future, considering cost savings. I believe such proactive users as us will be in the minority.

I don't mind the change, as we're unlikely to hit any weird CI issues. Also a good part of us devs are on ARM those days thanks to MacBooks.
Also, just for the curiosity's sake, it's quite interesting to how good CI run on ARM, and bring this experience to our primary jobs to save on ever-hungry CI.

[bquorning]

I was hoping that GitHub would provide something like the ubuntu-latest runner, e.g. ubuntu-arm-latest, that points to different OS versions so we wouldn’t have to keep updating it manually. And who knows, maybe it will be added? This is still early days; this is still a “public preview” feature that is subject to change.