Only tag `latest` for new releases not "nightly" pushes to master

[Dav1dde]

Relay tags every commit to master as latest on the GHCR image. We should only tag the latest release as latest, like we do in artifact registry or how sentry-cli does it.

We can do it in a release job like sentry-cli does it.

And we need to remove the current logic which tags master commits as latest (if not already happening, tag it as nightly instead).