ci: use almalinux instead of centos, add 9

[henryiii]

Description

AlmaLinux is used by manylinux, so let's use that here.

Suggested changelog entry:

None needed, CI.

[rwgk]

Do you think it would be useful to add this to the changelog?

Testing with Centos 8 was replaced with AlmaLinux 8. Testing with AlmaLinux 9 was added.

I think that would be useful to highlight in the changelog because from a practical viewpoint that means we are dropping support for Centos 8, but are adding support for AlmaLinux 8 & 9.

[henryiii]

Not really, we support RHEL 7, 8, and 9. We just use CentOS's repackaging for 7 and AlmaLinux repackaging for 8 & 9. We could use RockyLinux and it would be the same. Or, since I'm at Princeton, maybe Springdale. ;) For an end user, RHEL 7-9 is the important thing, not how it's been debranded and rebuilt.

[henryiii]

I also believe we don't advertise the list of OS's we build on, just compiler versions. Could be wrong though.

We are avoiding stream distros - I think we were supporting 8 stream, which we aren't now. But we are now testing on 9 anyway, and we've never supported¹/tested Fedora or even non LTS Ubuntu either.

Footnotes

1. Supported by testing. I'd assume they work, and I'd try to fix them on a best-effort basis if they didn't. ↩