Fix mock brain

ml-agents/mlagents/trainers/tests/mock_brain.py

             prev_action=prev_action,
             interrupted=max_step,
             memory=memory,
+            group_status=[],
+            group_reward=0,
         )
         steps_list.append(experience)
     obs = []
         prev_action=prev_action,
         interrupted=max_step_complete,
         memory=memory,
+        group_status=[],
+        group_reward=0,
-        steps=steps_list, agent_id=agent_id, behavior_id=behavior_id, next_obs=obs
+        steps=steps_list,
+        agent_id=agent_id,
+        behavior_id=behavior_id,
+        next_obs=obs,
+        next_group_obs=[],
     )