Update workflow

Author: charlescyt

.github/workflows/build.yml

@@ -10,6 +10,8 @@ on:
 jobs:
   build:
     runs-on: ubuntu-latest
+    permissions:
+      contents: write
 
     steps:
       - name: Git checkout
@@ -39,6 +41,7 @@ jobs:
 
       - name: Deploy to GitHub Pages
         uses: peaceiris/actions-gh-pages@v4
+        if: github.ref == 'refs/heads/main'
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
           publish_dir: ./build/web