Re-think `ci.yaml` dependencies between jobs

[michalrus]

Follow-up to:

• Update all deps + one CI #448 (comment)

Context

After we have a single ci.yaml file, it’s worth thinking about dependencies – this is what that workflow merge in #448 really gives us.

Do we want to:

• save GitHub minutes, and not pay for OCI builds that would fail because we saw that build_and_test,
• or have better developer turn-around time, but running as much as possible in parallel, even if all the builds would fail because of a single compilation error?

The same question about Hydra tests:

• maybe it makes sense to run them only if the PR is fine?
• OTOH, that will increase the total wall clock "build" time by 15 minutes, etc.