build: run workflows when a PR is ready for review

Add `ready_for_review` to the activity types for the pull_request event.

PR-URL: https://github.com/nodejs/node/pull/39405


Reviewed-By: Jiawen Geng <technicalcute@gmail.com>
Reviewed-By: Richard Lau <rlau@redhat.com>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>