Revise reminder messages about merge requests

What does this MR do and why?

Another message in policies/stages/hygiene/ that we could apply some light polish to. Revises the automated messages shown to users when:

• A merge request is labeled regression but lacks a version number
• A merge request prompts a GitLab team member to add labels.

It needs both a TW review (because I'm creating original work) and a review from Engineering Productivity.

Expected impact & dry-runs

These are strongly recommended to assist reviewers and reduce the time to merge your change.

Action items

• (If applicable) Add documentation to the handbook pages for Triage Operations =>
• (If applicable) Identify the affected groups and how to communicate to them:
  • /cc @person_or_group =>
  • Relevant Slack channels =>
  • Engineering week-in-review