This container can be pulled via:
  docker pull registry.opensuse.org/devel/bci/sle-15-sp7/containerfile/suse/nginx:1.21
  docker pull registry.opensuse.org/devel/bci/sle-15-sp7/containerfile/suse/nginx:1.21-51.2

Set DOCKER_CONTENT_TRUST=1 to enable image tag verification.