refactor: replace deprecated datetime.utcnow method

packages/valory/skills/decision_maker_abci/handlers.py

@@ -387,6 +387,6 @@ def _check_is_receiving_mech_responses(self) -> bool:
         # (an on chain transaction)
         return (
             self.synchronized_data.decision_receive_timestamp
-            < int(datetime.utcnow().timestamp())
+            < int(datetime.now(timezone.utc).timestamp())
             - self.context.params.expected_mech_response_time
         )