CI: Force Node.js 24 for action-pr-title

[rubambiza]

Summary

• Adds FORCE_JAVASCRIPT_ACTIONS_TO_NODE24=true to the PR verifier job
• Suppresses the Node.js 20 deprecation warning on all caller repos
• The action only uses @actions/core and @actions/github (string matching + one REST call), verified safe for Node 24

[rubambiza]

Suggestion from Humr review on a caller PR (humr#361): The caller workflow uses a generic job name verify — renaming it to verify-pr-title would make the check's purpose visible at a glance in the GitHub Actions panel.

This would be a change in each caller repo's pr-verifier.yml, not in this reusable workflow. I'll batch-update the caller PRs with the rename when pushing the SHA bump after this merges.