Update docs.yml

Author: flagarde

.github/workflows/docs.yml

@@ -75,6 +75,7 @@ jobs:
       name: github-pages
       url: ${{ steps.deployment.outputs.page_url }}
     runs-on: ubuntu-latest
+    if: github.ref == 'refs/heads/master'
     needs: docs
     steps:
       - name: Deploy to GitHub Pages