Consider pinning runner image instead of using ubuntu-latest in JIT CI #125560
Description
It looks like GitHub updated the default/latest Ubuntu runner to use Ubuntu 24.04 from 22.04, which is leading to failed CI runs. We should consider pinning the version here.
(GitHub's general guidance is to use ubuntu-latest, so if folks feel strongly against this, this could also be a temporary measure until the issue resolves.)
See also actions/runner-images#10788