Using Ruby 3.1 as default on GitLab SaaS Linux runners

This post announces the change of the default container image for GitLab SaaS Runners on Linux from Ruby 2.5 to Ruby 3.1, effective January 12, 2023. It explains that this change will only impact jobs that do not explicitly specify a container image in their `.gitlab-ci.yml` file. Users are advised to check their job logs for the current image and can test compatibility by configuring their jobs to use `image: ruby:3.1`. Future plans include defining a new container image maintenance process for GitLab SaaS Runners on Linux to ensure the default image is updated with the latest security fixes.