vagrant plugin in CI

I've started looking at adding back vagrant plugin in CI but not sure how to proceed:

- the vagrant plugin can only be tested on macosx-12 runner (nested virtualization support needed)
- the podman and docker plugin can't probably be tested with macosx-12
- the PYTEST_REQPASS will probably be different between linux and macosx runners so not sure how to deal with that as it would be nice to avoid duplication as most as possible in the workflow.

Also, ages ago, we used the (unreliable?) zuul ci to test with libvirt. Not sure what's the status of zuul ci these days ?

Start by reviewing the CI workflow and how the vagrant, podman, and docker plugins are currently selected for testing. Check the macosx-12 runner constraints and how PYTEST_REQPASS is set across Linux and macOS, then determine whether Zuul CI is still relevant. Done means vagrant coverage is restored without duplicating most workflow logic or breaking the other plugin tests.

Written by the indexing model from the issue text.