This container can be pulled via:
  docker pull registry.opensuse.org/devel/bci/sle-15-sp7/containerfile/bci/spack:0.21
  docker pull registry.opensuse.org/devel/bci/sle-15-sp7/containerfile/bci/spack:0.21.3
  docker pull registry.opensuse.org/devel/bci/sle-15-sp7/containerfile/bci/spack:0.21.3-3.4

Set DOCKER_CONTENT_TRUST=1 to enable image tag verification.