Make it possible to build with c++20 and switch to new Key4hep build action

[tmadlener]

BEGINRELEASENOTES

• Allow to build with c++20
• Switch to new key4hep build action and remove old workflow

ENDRELEASENOTES

[jmcarcell]

This will get overwritten if it's not changed in key4hep-actions. Why is this needed? With the push: they run whenever there is a push in a branch, in a PR or not, pull_request: will duplicate the jobs for a PR since they will run in the PR and after push meaning it takes longer to find workers and for all the jobs to run

[tmadlener]

👍 removed

[tmadlener]

Without the pull_request they will not report back to the PR. The push hook only runs them on the branch (which is in my fork). Maybe push: master and pull_request: is the way to go?

[jmcarcell]

Yes I think that's it. The repos have to have the same name for the default branch though but in this case it's true for key4hep

[jmcarcell]

Ah no I just remembered why I didn't go for that. With that, the workflows don't run in your workflow when you push to a different branch other than the default one and some people don't like that. I couldn't find a way of having it

• Run once in PRs
• Run also when pushing to a fork
• Report in the PR page
  The closest is the first two without the third one with only push:

[tmadlener]

OK. But the one that we definitely need is the reporting, right? Otherwise we cannot use auto-merge with required checks.

I also didn't find a way to restrict the push to only the main repository, which I guess would be nice, because then there would be no duplicate reporting of failures.

[jmcarcell]

The spack recipe was missing having the standard specified so it was being built with C++17 instead of C++20 for the nightlies