only build and publish docs if run on main

Author: Guen Prawiroatmodjo

.github/workflows/cd.yml

@@ -56,6 +56,7 @@ jobs:
     environment:
       name: github-pages
       url: ${{ steps.deploy-pages.outputs.page_url }}
+    if: github.ref == 'refs/heads/main'
     steps:
       - name: Checkout repo
         uses: actions/checkout@v4