Do not build unknown/unknown image

[zembrowski]

Currently an image for the OS/Arch: unknown/unknown is being built (cf. attached screenshot or example sub-page). Not sure how to prevent this.

Multi-arch build is set in .github/workflows/build-and-publish.yml#L65

[zembrowski]

Followed docker/build-push-action/issues/820#issuecomment-1486849546 and added:

provenance: false

as a temporary fix (with build-push-action@v4).