update documentation.yaml file

Author: haroon10725

.github/workflows/documentation.yaml

@@ -1,6 +1,9 @@
 name: documentation
 
-on: [push, pull_request, workflow_dispatch]
+on:
+  push:
+    branches: [main]
+  workflow_dispatch:
 
 permissions:
   contents: write
@@ -19,7 +22,10 @@ jobs:
           sphinx-build . _build/html
       - name: Deploy to GitHub Pages
         uses: peaceiris/actions-gh-pages@v3
-        if: ${{ github.event_name == 'push' && github.ref == 'refs/heads/main' }}
+        if: |
+          github.event_name == 'push' &&
+          github.ref == 'refs/heads/main' &&
+          startsWith(github.event.head_commit.message, 'Merge pull request')
         with:
           publish_branch: gh-pages
           github_token: ${{ secrets.GITHUB_TOKEN }}