Add missing six dep: docker/docker-py#2842

Author: geerlingguy

.github/workflows/build.yml

@@ -34,7 +34,7 @@ jobs:
           python-version: '3.x'
 
       - name: Install prerequisites.
-        run: pip3 install ansible docker
+        run: pip3 install ansible docker six
 
       - name: Install role dependencies.
         run: ansible-galaxy install -r requirements.yml
@@ -73,7 +73,7 @@ jobs:
           python-version: '3.x'
 
       - name: Install prerequisites.
-        run: pip3 install ansible docker
+        run: pip3 install ansible docker six
 
       - name: Install role dependencies.
         run: ansible-galaxy install -r requirements.yml