fix: return the first response when broadcasting to a single socket (#4878)

Author: BCCSTeam

lib/broadcast-operator.ts

@@ -254,7 +254,7 @@ export class BroadcastOperator<EmitEvents extends EventsMap, SocketData>
         clearTimeout(timer);
         ack.apply(this, [
           null,
-          this.flags.expectSingleResponse ? null : responses,
+          this.flags.expectSingleResponse ? responses[0] : responses,
         ]);
       }
     };