Fix nats tests after #1751 (#1753)

* In case if core-subscriber receive a JetStream message.

* Remove default value and add tests

* Fix nats tests after #1751

faststream/nats/testing.py

@@ -63,7 +63,7 @@ class FakeProducer(NatsFastProducer):
     def __init__(self, broker: NatsBroker) -> None:
         self.broker = broker
 
-        default = NatsParser(pattern="")
+        default = NatsParser(pattern="", no_ack=False)
         self._parser = resolve_custom_func(broker._parser, default.parse_message)
         self._decoder = resolve_custom_func(broker._decoder, default.decode_message)