ci: restrict deploy job to push events only

Only run the deploy job on push to main, not on pull requests.

Author: thewtex

.github/workflows/build.yml

@@ -57,6 +57,7 @@ jobs:
 
   deploy:
     needs: build
+    if: github.event_name == 'push' && github.ref == 'refs/heads/main'
     runs-on: ubuntu-latest
     permissions:
       pages: write