[BugFix] Fix single action pass to gym when action key is not "action"

ghstack-source-id: b91b9e1
Pull-Request-resolved: pytorch#2942

Author: Vincent Moens

torchrl/envs/gym_like.py

@@ -231,7 +231,11 @@ def read_action(self, action):
         Returns: an action in a format compatible with the contained environment.
 
         """
-        return self.action_spec.to_numpy(action, safe=False)
+        action_spec = self.full_action_spec
+        action_keys = self.action_keys
+        if len(action_keys) == 1:
+            action_spec = action_spec[action_keys[0]]
+        return action_spec.to_numpy(action, safe=False)
 
     def read_done(
         self,