Specify src path for isort. (#8867)

demo/dask/gpu_training.py

@@ -7,10 +7,10 @@ from dask import array as da
 from dask import dataframe as dd
 from dask.distributed import Client
 from dask_cuda import LocalCUDACluster
-from xgboost.dask import DaskDMatrix
 
 import xgboost as xgb
 from xgboost import dask as dxgb
+from xgboost.dask import DaskDMatrix
 
 
 def using_dask_matrix(client: Client, X, y):