Ouch this was a bad one. We’ve been installing test gems in production since forever.
Fixed in
https://github.com/discourse/discourse_docker/commit/b8866fb9bbda41b643dd1acf9798b230b75ddb62
https://github.com/discourse/docker_manager/commit/79aa85a88a15836ec881bb91c321978434c2f85a
We’re releasing a new base image soon to fix this issue once you rebuild.