CI: Add script to post mastodon toots for commits on master

This patch adds the toot-commits script (mirroring tweet-commits),
posting new commits on the master branch to
https://serenityos.social/@commits.

.github/workflows/social-media.yml

@@ -1,4 +1,4 @@
-name: Twitter notifications
+name: Social media notifications
 
 on: [ push ]
 
@@ -22,3 +22,20 @@ jobs:
           CONSUMER_SECRET: ${{ secrets.CONSUMER_SECRET }}
           ACCESS_TOKEN: ${{ secrets.ACCESS_TOKEN }}
           ACCESS_TOKEN_SECRET: ${{ secrets.ACCESS_TOKEN_SECRET }}
+
+  notify_mastodon:
+    runs-on: ubuntu-22.04
+    if: always() && github.repository == 'SerenityOS/serenity' && github.ref == 'refs/heads/master'
+
+    steps:
+      - uses: actions/checkout@v3
+      - uses: actions/setup-node@v3
+        with:
+          node-version: '14'
+      - run: npm i mastodon
+      - run: |
+          node ${{ github.workspace }}/Meta/toot-commits.js << 'EOF'
+          ${{ toJSON(github.event) }}
+          EOF
+        env:
+          ACCESS_TOKEN: ${{ secrets.MASTODON_ACCESS_TOKEN }}