src-cli: fix latest version release detection

[courier-new]

Releasing src-cli 4.1 didn't go exactly as planned because the release action identified the wrong tag for the most recent one. It turns out that the way the src-cli repo is cloned into the container for the first job, it resets the git tag taggerdates, so git tag --sort=taggerdate isn't a reliable sort mechanism for getting the most recent tag.

We should be able to fix this by using the GitHub environment variable that is available during the action, GITHUB_REF_NAME, instead. But this is slightly annoying, because the change is only testable when a new tag is pushed.

This issue encompasses the work to make the fix, set up a state to test it in, and teardown afterwards.