Container registry lists the architecture unknown/unknown when manifest attestations are present

[KN4CK3R]

Related:
https://github.com/orgs/community/discussions/45969
docker/build-push-action#755
https://codeberg.org/forgejo/forgejo/issues/780

I recently noticed that packages that have been pushed to the container registry using docker buildx build now have a new architecture listed, unknown/unknown. After some further investigation, I discovered that what is happening is that the Docker Buildx CLI is including image attestations for these images, which seems harmless, but causes GitHub Packages to list the unknown/unknown arch used for these attestations under the "OS / Arch" tab. This is similar to another topic recently posted, but this is more of a UI bug rather than an issue inspecting or pulling the manifests.

The current behavior means that if you push an image for linux/arm64 and linux/amd64, you'll get three architectures listed, linux/arm64, linux/amd64, and unknown/unknown. The unknown/unknown arch has a hash listed, but that is not shown in the version list anywhere unless you dig deep to find it. This appears to inconsistent with what the Docker Hub shows, which, in this case, would be only two architectures linux/arm64 and linux/amd64.