change build dir for gh-pages

Author: thomas loubrieu

.github/workflows/publish-docs.yml

@@ -22,4 +22,4 @@ jobs:
         uses: peaceiris/actions-gh-pages@v3
         with:
           github_token: ${{ secrets.GITHUB_TOKEN }}
-          publish_dir: ./docs
+          publish_dir: ./docs/_build/html