[Chapel Merge] Refactor commit emailer workflow to avoid `pull_request_target`

Failure encountered generating PR merge email for commit 266fd432711d873ef2c140001ab54acc9e5b14f1.

Run ID: 38460294809

This failure is due to a typo I introduced in my PR refactoring the email workflow, Refactor commit emailer workflow to avoid `pull_request_target` by arifthpe · Pull Request #29362 · chapel-lang/chapel · GitHub. It has been fixed in follow up PR Fix missed variable rename in emailer workflow by arifthpe · Pull Request #29524 · chapel-lang/chapel · GitHub, and the email dispatched for that PR seems to have worked properly.