Specify src path for isort. (#8867)

tests/python/test_updaters.py

@@ -5,6 +5,9 @@ from typing import Any, Dict, List
 import numpy as np
 import pytest
 from hypothesis import given, note, settings, strategies
+
+import xgboost as xgb
+from xgboost import testing as tm
 from xgboost.testing.params import (
     cat_parameter_strategy,
     exact_parameter_strategy,
@@ -12,9 +15,6 @@ from xgboost.testing.params import (
 )
 from xgboost.testing.updater import check_init_estimation, check_quantile_loss
 
-import xgboost as xgb
-from xgboost import testing as tm
-
 
 def train_result(param, dmat, num_rounds):
     result = {}