Skip review apps when RUBY_VERSION == "3.0"

Goal

Skip review apps when RUBY_VERSION == "3.0"

Background

It is not ideal that we don't run review apps for Ruby 3.0 for now, but it has some issues at the moment:

• There's some difficulties passing the variables to the downstream review pipeline: !90438 (comment 1010683850) Without being able to properly pass the variables downstream, the review apps cannot run in Ruby 3.0
• We want to run a scheduled Ruby 3.0 pipeline: #340298 (closed) However, running it so frequently along with Ruby 2.7 pipeline, causing review apps instability due to stepping on each others: https://gitlab.com/gitlab-com/quality/engineering-productivity/-/issues/7#note_1024381740 (We may resolve this by increasing the gaps, but that's not very ideal and can still be problematic given that the schedule might not be so accurate: https://gitlab.com/gitlab-com/quality/engineering-productivity/-/issues/7#note_1025261816)

Bonus

If bonus weren't done, let's create follow up issues for them.

• We also want to receive a Slack message in #f_ruby3 when the Ruby 3.0 scheduled pipeline failed. We can add this in .gitlab/ci/notify.gitlab-ci.yml via scripts/slack.
  • Bonus bonus: If we can run this in another branch, not the default branch, it would be even better. However the branch should be up-to-date with the default branch. It's fine to have some delays but it should not be a manual work.