Update cattrs dependencies to support python3.9 (#4821)

com.unity.ml-agents/CHANGELOG.md

 #### com.unity.ml-agents / com.unity.ml-agents.extensions (C#)
 #### ml-agents / ml-agents-envs / gym-unity (Python)
 - The `encoding_size` setting for RewardSignals has been deprecated. Please use `network_settings` instead. (#4982)
+- The `cattrs` version dependency was updated to allow `>=1.1.0` on Python 3.8 or higher. (#4821)
+
 ### Bug Fixes
 #### com.unity.ml-agents (C#)
 #### ml-agents / ml-agents-envs / gym-unity (Python)

ml-agents-envs/mlagents_envs/tests/test_envs.py

     )
     env = UnityEnvironment(file_name=file_name, worker_id=0, base_port=base_port)
     assert expected == env._port
+    env.close()
 
 
 @mock.patch("mlagents_envs.env_utils.launch_executable")
     args = env._executable_args()
     log_file_index = args.index("-logFile")
     assert args[log_file_index + 1] == "./some-log-folder-path/Player-0.log"
+    env.close()
 
 
 @mock.patch("mlagents_envs.env_utils.launch_executable")

ml-agents-envs/mlagents_envs/tests/test_rpc_utils.py

 import io
 import numpy as np
 import pytest
-from typing import List, Tuple
+from typing import List, Tuple, Any
 
 from mlagents_envs.communicator_objects.agent_info_pb2 import AgentInfoProto
 from mlagents_envs.communicator_objects.observation_pb2 import (
         reward = decision_steps.reward[agent_id_index]
         done = False
         max_step_reached = False
-        agent_mask = None
+        agent_mask: Any = None
-            agent_mask = []  # type: ignore
+            agent_mask = []
+            agent_mask = agent_mask.astype(np.bool).tolist()
         observations: List[ObservationProto] = []
         for all_observations_of_type in decision_steps.obs:
             observation = all_observations_of_type[agent_id_index]
             reward=reward,
             done=done,
             id=agent_id,
-            max_step_reached=max_step_reached,
+            max_step_reached=bool(max_step_reached),
             action_mask=agent_mask,
             observations=observations,
         )
             reward=reward,
             done=done,
             id=agent_id,
-            max_step_reached=max_step_reached,
+            max_step_reached=bool(max_step_reached),
             action_mask=None,
             observations=final_observations,
         )

ml-agents/setup.py

         # https://github.com/Unity-Technologies/ml-agents/blob/main/docs/Installation.md#windows-installing-pytorch
         'torch>=1.6.0,<1.8.0;platform_system!="Windows"',
         "tensorboard>=1.15",
-        # cattrs 1.1.0 dropped support for python 3.6.
-        "cattrs>=1.0.0,<1.1.0",
+        # cattrs 1.1.0 dropped support for python 3.6, but 1.0.0 doesn't work for python 3.9
+        # Since there's no version that supports both, we have to draw the line somwehere.
+        "cattrs<1.1.0; python_version<'3.8'",
+        "cattrs>=1.1.0; python_version>='3.8'",
         "attrs>=19.3.0",
         'pypiwin32==223;platform_system=="Windows"',
         "importlib_metadata; python_version<'3.8'",