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: #39825
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

.github/workflows/find-inactive-collaborators.yml

@@ -28,3 +28,14 @@ jobs:
 
       - name: Find inactive collaborators
         run: tools/find-inactive-collaborators.mjs ${{ env.NUM_COMMITS }}
+
+      - name: Open pull request
+        uses: gr2m/create-or-update-pull-request-action@v1
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        with:
+          author: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
+          body: This PR was generated by tools/find-inactive-collaborators.yml.
+          commit-message: "meta: move one or more collaborators to emeritus"
+          labels: meta
+          title: "meta: move one or more collaborators to emeritus"