fix policy action_spec typo

ml-agents/mlagents/trainers/torch/model_serialization.py

         )
 
         self.output_names = ["version_number", "memory_size"]
-        if self.policy.action_spec.continuous_size > 0:
+        if self.policy.behavior_spec.action_spec.continuous_size > 0:
-        if self.policy.action_spec.discrete_size > 0:
+        if self.policy.behavior_spec.action_spec.discrete_size > 0:
-            self.policy.action_spec.continuous_size == 0
-            or self.policy.action_spec.discrete_size == 0
+            self.policy.behavior_spec.action_spec.continuous_size == 0
+            or self.policy.behavior_spec.action_spec.discrete_size == 0
         ):
             self.output_names += [
                 "action",