tools: update workflow to open a pull request

Now that find-inactive-collaborators.mjs automates the README.md changes
to move the inactive collaborators to the emeriti section, update the
GitHub Actions workflow to open a pull request.

PR-URL: https://github.com/nodejs/node/pull/39825


Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>