CI: Upgrade to cimg/ not circleci/ images
CI: Upgrade to cimg/ not circleci/ images

https://circleci.com/developer/images/image/cimg/ruby notes that these
images are the more modern ones.

In deploy, we use: cimg/ruby:3.0. That is an alias to the latest 3.0 Docker image.

barsoom/pipeline,barsoom/pipeline,barsoom/pipeline,barsoom/pipeline