ci: install graphviz for docs build

.github/workflows/docs.yml

@@ -3,7 +3,7 @@ name: Deploy documentation
 on:
   workflow_dispatch:
   push:
-    tags:        
+    tags:
       - 'v[0-9]\.[0-9]+\.[0-9]+'
 
 jobs:
@@ -15,26 +15,29 @@ jobs:
       id-token: write
 
     steps:
-    - uses: actions/checkout@v4
+      - uses: actions/checkout@v4
 
-    - name: Install uv and set the python version
-      uses: astral-sh/setup-uv@v6
-      with:
-        python-version: ${{ matrix.python-version }}
-      
-    - name: Build documentation
-      run: |
-        cd docs
-        uv run make html
-    
-    - name: Setup Pages
-      uses: actions/configure-pages@v5
-      
-    - name: Upload Pages artifact
-      uses: actions/upload-pages-artifact@v3
-      with:
-        path: 'docs/_build/html/'
+      - name: Install uv and set the python version
+        uses: astral-sh/setup-uv@v6
+        with:
+          python-version: ${{ matrix.python-version }}
 
-    - name: Deploy to GitHub Pages
-      id: deployment
-      uses: actions/deploy-pages@v4
+      - name: Install graphviz
+        run: sudo apt-get install -y graphviz
+
+      - name: Build documentation
+        run: |
+          cd docs
+          uv run make html
+
+      - name: Setup Pages
+        uses: actions/configure-pages@v5
+
+      - name: Upload Pages artifact
+        uses: actions/upload-pages-artifact@v3
+        with:
+          path: "docs/_build/html/"
+
+      - name: Deploy to GitHub Pages
+        id: deployment
+        uses: actions/deploy-pages@v4