From prow runs:

W0406 17:26:48.478] WARNING: gcloud docker will not be supported for Docker client versions above 18.03. Please use gcloud auth configure-docker to configure docker to use gcloud as a credential helper, then use docker as you would for non-GCR registries, e.g. docker pull gcr.io/project-id/my-image. Add --verbosity=error to silence this warning, e.g. gcloud docker --verbosity=error -- pull gcr.io/project-id/my-image. See: https://cloud.google.com/container-registry/docs/support/deprecation-notices#gcloud-docker