Just like in all other repos making Docker images.
The following tasks finish our ARM support and depend on each other:
* [ ] Push only one Docker image at the same time (this PR)
* [ ] GHA repo: auto-create not just X.Y.Z tags, but also X.Y, X and latest
* [ ] GHA repo: build multi-platform images
Deriving X.Y from X.Y.Z is easy. Also nobody releases a vX.Y.Z and a
vX.Y.{Z+1} at the same time. But a vX.Y.Z and a vX.{Y+1}.0 is likely.
Both check Docker Hub, both get green light and both push :latest. Who wins?