Update documentation.yml

Author: ZiyiXia

.github/workflows/documentation.yml

@@ -19,7 +19,7 @@ jobs:
           sphinx-build docs/source docs/build
       - name: Deploy to GitHub Pages
         uses: peaceiris/actions-gh-pages@v3
-        if: ${{ github.event_name == 'push' && github.ref == 'refs/heads/main' }}
+        if: ${{ github.event_name == 'push' && github.ref == 'refs/heads/master' }}
         with:
           publish_branch: gh-pages
           github_token: ${{ secrets.GITHUB_TOKEN }}