refactor: use new port negotiation style

As changed in the API document, this now uses the new port negotiation style.

ref: N25B-168

src/robot_interface/endpoints/main_receiver.py

@@ -15,7 +15,7 @@ class MainReceiver(ReceiverBase):
         :param port: The port to use.
         :type port: int
         """
-        super(MainReceiver, self).__init__("main", "json")
+        super(MainReceiver, self).__init__("main")
         self.create_socket(zmq_context, zmq.REP, port, bind=False)
 
     @staticmethod