gh-125560: Pin JIT CI to ubuntu-22.04

[savannahostrowski]

Ideally, we'd pin to 24.04 but that seems to be broken right now. We can probably bump the version once some rough edges get ironed out in a couple weeks?

I did a little test run here https://github.com/savannahostrowski/cpython/actions/runs/11357983419/job/31591954044?pr=5 and everything looked good except x86_64-pc-windows-msvc (unrelated for obvious reasons and being handled in #125217)

(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.)

• Issue: Consider pinning runner image instead of using ubuntu-latest in JIT CI #125560

[hugovk]

@savannahostrowski Are there still failures with 24.04? If so, let's merge and revisit upgrading later.

[Eclips4]

FYI, test_embed failure is a known thing, see #126255 for more information

[hugovk]

Looks like we still have stuff to figure out with #126255 etc., but let's merge just to pin to something, especially if ubuntu-latest is mid-rollout from 22.04 -> 24.04, and see also actions/runner-images#10636 (comment).

Let's merge, we can change to 24.04 later when we're ready.