Update the Ruby 2.7 pipelines to 3.1

What does this MR do and why?

This MR changes the current Ruby 2.7 pipelines we have with Ruby 3.1 pipelines.

Here are the ruby3_1 branch and ruby3_1-sync branch. After this, we still have to:

• Create a RUBY3_1_SYNC_TOKEN (we can rename RUBY2_SYNC_TOKEN)
• Create new Update ruby 2 scheduled pipelines to ruby 3 alternative: https://gitlab.com/gitlab-org/gitlab/-/pipeline_schedules
  • Sync ruby3_1 branch every odd hour (Target ruby3_1-sync)
  • Run ruby3_1 pipeline every odd hour 5 minutes after sync
  • Nightly ruby3_1
• For this we could probably just update the ruby2 scheduled pipelines to point to ruby3_1 and ruby3_1-sync branches instead

I ran the pipeline with label pipeline:run-in-ruby3_1 (https://gitlab.com/gitlab-org/gitlab/-/pipelines/924048806), and it seems to run in Ruby 3.1

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.

Related to #414658 (closed)