release: integrate (git-annex) tests into release process

[kousu]

Now that #13 is merged, work it into release-action so that releases are gated on the tests passing.

[kousu]

We should be able to use git-annex-tests.yml as a reusable workflow in the test branch. I think I'll need to rearrange the code though, since there's currently a bash-if in there that checks if the release needs to be made; but I can't call out to a workflow from bash, so I'll need to split that up and use some Workflow ifs.