fix: Pass message_length param. Addresses a2aproject/A2A#861

Author: kthota-g

src/a2a/client/transports/grpc.py

@@ -138,7 +138,10 @@ async def get_task(
     ) -> Task:
         """Retrieves the current state and history of a specific task."""
         task = await self.stub.GetTask(
-            a2a_pb2.GetTaskRequest(name=f'tasks/{request.id}')
+            a2a_pb2.GetTaskRequest(
+                name=f'tasks/{request.id}',
+                history_length=request.history_length,
+            )
         )
         return proto_utils.FromProto.task(task)