Add PCL for the Ruby 3 upgrade for GitLab.com

Why is this change being made?

Add PCL for the Ruby 3 upgrade on SaaS

Delivery is requesting a Hard PCL on 2023-03-07 to ensure the platform stability while upgrading GitLab.com to Ruby 3. The exact times will be decided later on to ensure proper coverage.

• Change request associated: gitlab-com/gl-infra/production#5494 (closed)
• Deployment strategy on: gitlab-com/gl-infra/delivery#2749 (closed)
• Epic to rollout Ruby 3 to .com and self-managed: gitlab-com/gl-infra&865 (closed)

Author Checklist

• Provided a concise title for this Merge Request (MR)
• Added a description to this MR explaining the reasons for the proposed change, per say why, not just what
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  • The when to get approval handbook section explains the workflow in more detail
• If the changes affect team members, or warrant an announcement in another way, please consider posting an update in #whats-happening-at-gitlab linking to this MR
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