CI jobs fail because of docker.io pull rate limit

Example: https://gitlab.torproject.org/tpo/tpa/puppet-weblate/-/jobs/846620

ERROR: Job failed: failed to pull image "ruby:2.7.2" with specified policies
[always if-not-present]: initializing source docker://ruby:2.7.2: reading
manifest 2.7.2 in docker.io/library/ruby: toomanyrequests: You have reached your
pull rate limit. You may increase the limit by authenticating and upgrading:
https://www.docker.com/increase-rate-limit (manager.go:254:126s)