Improve efficiency of running the most simple CI/CD builds
## Description Slack: https://gitlab.slack.com/archives/C0SFP840G/p1681376329482399 We are still using a `ruby:3.1` image as a default one, even when someone does not specify an `image:` in their `.gitlab-ci.yml` at all. It appears that we are not caching the image, because pulling it still takes 30+ seconds in a simple hello world build on GitLab.com: ```yaml # .gitlab-ci.yml hello: script: echo "Hello World" ``` ## Proposal We should cache the default image and other, most popular ones by default, to reduce the time to start `script` block execution on shared runners. **This may increase the speed of very simple builds by at least 50%.** /cc @tmaczukin @clefelhocz1 @nicolewilliams
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