Specify src path for isort. (#8867)

tests/python-gpu/test_gpu_data_iterator.py

@@ -2,6 +2,7 @@ import sys
 
 import pytest
 from hypothesis import given, settings, strategies
+
 from xgboost.testing import no_cupy
 
 sys.path.append("tests/python")

tests/python-gpu/test_gpu_eval_metrics.py

@@ -1,10 +1,10 @@
 import sys
 
 import pytest
-from xgboost.testing.metrics import check_quantile_error
 
 import xgboost
 from xgboost import testing as tm
+from xgboost.testing.metrics import check_quantile_error
 
 sys.path.append("tests/python")
 import test_eval_metrics as test_em  # noqa

tests/python-gpu/test_gpu_prediction.py

@@ -3,10 +3,10 @@ import sys
 import numpy as np
 import pytest
 from hypothesis import assume, given, settings, strategies
-from xgboost.compat import PANDAS_INSTALLED
 
 import xgboost as xgb
 from xgboost import testing as tm
+from xgboost.compat import PANDAS_INSTALLED
 
 if PANDAS_INSTALLED:
     from hypothesis.extra.pandas import column, data_frames, range_indexes

tests/python-gpu/test_gpu_updaters.py

@@ -4,11 +4,11 @@ from typing import Any, Dict
 import numpy as np
 import pytest
 from hypothesis import assume, given, note, settings, strategies
-from xgboost.testing.params import cat_parameter_strategy, hist_parameter_strategy
-from xgboost.testing.updater import check_init_estimation, check_quantile_loss
 
 import xgboost as xgb
 from xgboost import testing as tm
+from xgboost.testing.params import cat_parameter_strategy, hist_parameter_strategy
+from xgboost.testing.updater import check_init_estimation, check_quantile_loss
 
 sys.path.append("tests/python")
 import test_updaters as test_up