ci: Re-enable Review Apps

What does this MR do and why?

Now that we identified the root cause of instabilities of the Review Apps cluster, and put some mitigation in place (gitlab-org/quality/engineering-productivity/team#116 (comment 1179429380)), we're ready to enable Review Apps again.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.