Update documentation setup

Author: Aaron-Hsieh-0129

.github/workflows/documentation.yml

@@ -1,6 +1,11 @@
 name: documentation
 
-on: [push, pull_request, workflow_dispatch]
+on:
+  push:
+    branches:
+      - main
+  pull_request:
+  workflow_dispatch:
 
 permissions:
   contents: write
@@ -24,4 +29,4 @@ jobs:
           publish_branch: gh-pages
           github_token: ${{ secrets.GITHUB_TOKEN }}
           publish_dir: _build/
-          force_orphan: true
+          force_orphan: true