updated gh workflow to install graphviz

Signed-off-by: Pedro Escaleira <pedroescaleira@hotmail.com>

Author: oEscal

.github/workflows/python-ci.yml

@@ -16,6 +16,10 @@ jobs:
       - uses: "actions/setup-python@a26af69be951a213d495a4c3e4e4022e16d87065" # v5.6.0
         with:
           python-version: '3.9'
+      - name: Install graphviz
+        run: |
+          sudo apt-get update
+          sudo apt-get install graphviz graphviz-dev
       - name: Install dependencies
         run: |
           pip install pipenv