Applied suggestion

Author: fniephaus

.github/workflows/build-site.yml

@@ -50,7 +50,7 @@ jobs:
           path: docs/site/_site
 
   deploy:
-    if: github.event_name != 'pull_request' && github.ref == 'refs/heads/master'
+    if: github.event_name == 'push' && github.ref == 'refs/heads/master'
     needs: build
     runs-on: ubuntu-latest
     environment: