Cache manifest lists can now be exported to ghcr.io

:wave: You can now export a Docker buildx cache to ghcr.io from container builds. We’ve seen a few errors reported like this Cannot push cache layer to GHCR

If you had previously received an error exporting cache which looks like this:

------
 > exporting cache:
------
failed to solve: rpc error: code = Unknown desc = error writing manifest blob: failed commit on ref "sha256:...": unexpected status: 400 Bad Request

That export cache command will now succeed as expected and ghcr.io will serve the build cache when used as cache-from during building as well.

For example this buildx command uses cache-from:

docker buildx build
    --progress plain
    --load 
    f Dockerfile
    -t ghcr.io/github/container-registry-playground:build-x
    --pull
    --cache-from=type=registry,ref=ghcr.io/github/container-registry-playground:build
    --cache-to=type=registry,ref=ghcr.io/github/container-registry-playground:build,mode=max .

Hi, Bryan!

Is it possible to give slightly more information about this feature? What exactly did you fix to support exporting cache from buildkit?