Downgrade review-apps image to ruby 3.0

Context

Jobs like https://gitlab.com/gitlab-org/gitlab/-/jobs/6868149282 show that the review-app container image isn't available with ruby 3.1. It will be updated in gitlab-build-images!809 (closed).

What does this MR do and why?

Downgrade review-apps image to ruby 3.0

The ruby 3.1 image doesn't exist yet.

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