build arm images on arm workers

[minrk]

now that we have native arm workers, I think this should work the same as using circleci for arm, but all on GHA with a simpler task graph.

I really feel like this should be simpler, and deleting the intermediates still don't seem to work due to permission issues. Maybe there's a way to merge manifests before pushing, but we need to get the manifest from the build job to the publish job.

[jorgensd]

We also thought about this @minrk.
I have a workflow at:
https://github.com/jorgensd/dolfinx-tutorial/blob/main/.github/workflows/publish_docker.yml
That might be slightly simpler (but it does push before merging).

[minrk]

Nice, I think that probably is simpler