CI: publish correct directory

Author: tacaswell

.github/workflows/docs.yml

@@ -25,5 +25,5 @@ jobs:
         uses: peaceiris/actions-gh-pages@v3
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
-          publish_dir: ./docs/build/html
+          publish_dir: ./docs/build/singlehtml
           force_orphan: true