Update Release Checklist template

What does this MR do?

Another iteration of updating of https://gitlab.com/gitlab-org/gitlab-runner/blob/master/.gitlab/issue_templates/Release%20Checklist.md.

Will contain updates after handling the %10.8 release.

Why was this MR needed?

Are there points in the code the reviewer needs to double check?

Does this MR meet the acceptance criteria?

• Documentation created/updated
• Tests
  • Added for this feature/bug
  • All builds are passing
• Branch has no merge conflicts with master (if you do - rebase it please)

What are the relevant issue numbers?