Release checklist for 2.0.20

[jrfnl]

PRs to cherrypick into the next 2.0.x release (if there will be one):

• Tighten up the GitHub Actions workflow permissions #1048
• GH Actions: fail "setup-php" if requested tooling could not be installed #1067
• GH Actions: Bump ruby/setup-ruby from 1.319.0 to 1.321.0 in the action-runners group across 1 directory #1073