message: Use new `az acr repository delete --image` syntax
  The old syntax for deleting by a manifest no longer works with newer
  versions of the az CLI tool. This switches to the newer `--image
  repository@manifest` syntax.
diff: @@ -92,11 +92,11 @@ def get_image_manifests() -> Iterable[ImageManifest]:
  return [ImageManifest(**o) for o in manifests]
  def delete_image_by_manifest(manifest: ImageManifest) -> None:
  - """Delete a ACR image (and all its tags)."""
  + """Delete an ACR image (and all its tags)."""
  + image_name = '{}@{}'.format(REPOSITORY_NAME, manifest.digest)
  az_delete_cmd_line = ['az', 'acr', 'repository', 'delete',
  '--name', REGISTRY_NAME,
  - '--repository', REPOSITORY_NAME,
  - '--manifest', manifest.digest,
  + '--image', image_name,
  '--yes']
  _LOGGER.debug('Invoking %s', az_delete_cmd_line)
  p = subprocess.run(az_delete_cmd_line, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
  