ci: Disable Review Apps until it's stable again

What does this MR do and why?

Because of https://gitlab.com/gitlab-org/quality/engineering-productivity-infrastructure/-/issues/35, review apps aren't even accessible so it's better to completely disable them for now.

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.