This container can be pulled via:
  docker pull registry.opensuse.org/devel/bci/sle-15-sp6/containerfile/bci/spack:0.21
  docker pull registry.opensuse.org/devel/bci/sle-15-sp6/containerfile/bci/spack:0.21-20.5
  docker pull registry.opensuse.org/devel/bci/sle-15-sp6/containerfile/bci/spack:0.21.2
  docker pull registry.opensuse.org/devel/bci/sle-15-sp6/containerfile/bci/spack:0.21.2-20.5
  docker pull registry.opensuse.org/devel/bci/sle-15-sp6/containerfile/bci/spack:latest

Set DOCKER_CONTENT_TRUST=1 to enable image tag verification.