workflows: Update release container registry
workflows: Update release container registry

With [1] the release container moved from dockerhub to GitHub's
container registry, as we both build and use it from GitHub. This avoids
running into docker.io pull limits.

https://github.com/cockpit-project/cockpituous/pull/353

Closes #1180
jkozol/welder-web,weldr/welder-web,jkozol/welder-web,weldr/welder-web,weldr/welder-web,weldr/welder-web,jkozol/welder-web,jkozol/welder-web