Update python.yml

.github/workflows/python.yml

@@ -54,7 +54,7 @@ jobs:
     - name: Install dependencies
       run: |
         python -m pip install --upgrade pip
-        pip install flake8 pytest requests_mock graphql-core
+        pip install flake8 pytest requests_mock graphql-core six
         pip install .
 
     - name: Lint with flake8