[takayamaki]

ubuntu-latest is rolling over from 24.04 to 26.04.
On 26.04, ruby/setup-ruby has no build for Ruby 2.7, 3.0 and 3.1, so those jobs fail:

Error: Unavailable version 2.7.8 for ruby on ubuntu-26.04

See ruby/setup-ruby#954.
Builds for 26.04 are planned only for supported Ruby versions.

The runs on this repository still get 24.04 for now, but a run on my fork already got 26.04.
This change pins the runner to ubuntu-24.04, so the matrix keeps testing Ruby 2.7 to 3.1.
ubuntu-24.04 should stay available for a few more years.

Dropping Ruby 2.7 to 3.1 from the matrix is another option.
I kept them here, because some users may still be on those versions.

[geemus]

@takayamaki oops, I also saw this error and just fixed it by dropping the EOL rubies. I think I prefer staying on latest ubuntu and not officially supporting EOL ruby (making them best effort instead). Thanks!

[takayamaki]

@geemus
Thanks. I agree with the policy: stay on ubuntu-latest and keep EOL Rubies as best effort.

But the current matrix will still break.
ruby-builder has no Ruby 3.1.7 binary for ubuntu-26.04 either.
https://github.com/ruby/ruby-builder/releases/tag/ruby-3.1.7

The setup-ruby README says ubuntu-26.04 only has builds of CRuby 3.2 and newer, as older versions do not compile on it.
https://github.com/ruby/setup-ruby#supported-platforms

The 3.1 job passed only because the runner is still on 24.04 for now.
Once ubuntu-latest moves to 26.04, the 3.1 job will fail with the same error.
Dropping 3.1 seems the simplest fix.
3.2 is also EOL since April, but it still builds on 26.04, so that one is up to you.

[geemus]

oops, yes. I intended to drop 3.1 also and just accidentally missed it. I'll do that presently.

[geemus]

should be done now, good catch