Update sphinx.yaml

Author: slaizet

.github/workflows/sphinx.yaml

@@ -7,6 +7,8 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - uses: actions/checkout@v3
+    - name: Install graphviz
+      run: sudo apt install graphviz
     - name: Build HTML
       uses: ammaraskar/sphinx-action@master
     - name: Upload artifacts
@@ -19,4 +21,4 @@ jobs:
       if: github.ref == 'refs/heads/main'
       with:
         github_token: ${{ secrets.SYL_LAI }}
-        publish_dir: docs/build/html
+        publish_dir: docs/build/html