CI workflows should have a single job as the pass/fail gate

[thejpster]

Github requires us to type job names into the UI to set the pass/fail criteria for a PR build. This makes changing job names very difficult to synchronise (you have to merge a failing PR and then fix the UI after the fact).

rust-embedded/aarch32-cpu has a single job to indicate "pass/fail", and all the other jobs feed into it. For reasons, the job is "skipped on pass, failed on fail" but the UI is fine with that.

We should do that with this repo.

[rursprung]

i have for quite a while been using this pattern in all repos i maintain: https://github.com/rust-embedded-community/tb6612fng-rs/blob/master/.github/workflows/CI.yml#L99-L113
so far, this worked really well for me