Specify src path for isort. (#8867)

demo/nvflare/custom/controller.py

@@ -4,7 +4,6 @@ Example of training controller with NVFlare
 """
 import multiprocessing
 
-import xgboost.federated
 from nvflare.apis.client import Client
 from nvflare.apis.fl_context import FLContext
 from nvflare.apis.impl.controller import Controller, Task
@@ -12,6 +11,8 @@ from nvflare.apis.shareable import Shareable
 from nvflare.apis.signal import Signal
 from trainer import SupportedTasks
 
+import xgboost.federated
+
 
 class XGBoostController(Controller):
     def __init__(self, port: int, world_size: int, server_key_path: str,