add graphviz

Author: jaapio

.github/workflows/push.yml

@@ -54,6 +54,8 @@ jobs:
           restore-keys: |
             all-tools-${{ github.sha }}-
             all-tools-
+      - name: Install graphviz
+        run: apt-get update && apt-get install -y graphviz
       - name: Setup PHP
         uses: shivammathur/setup-php@master
         with: