Release checklist for 2.0.20

[jrfnl]

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

• CS/QA: prefer pre-increment over post-increment #694
• Update to WordPressCS 3.0.0 #832
• Composer: bump minimum versions for some dependencies #920
• 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
• 🔏 Update certificate bundle #1076
• Skip the SNI test until it can verify SNI again #1078