Require isort on all Python files. (#8420)

tests/python/test_demos.py

@@ -1,7 +1,7 @@
 import os
 import subprocess
-import tempfile
 import sys
+import tempfile
 
 import pytest
 

tests/python/test_tracker.py

@@ -5,9 +5,8 @@ import numpy as np
 import pytest
 
 import xgboost as xgb
-from xgboost import RabitTracker
+from xgboost import RabitTracker, collective
 from xgboost import testing as tm
-from xgboost import collective
 
 if sys.platform.startswith("win"):
     pytest.skip("Skipping dask tests on Windows", allow_module_level=True)

tests/python/test_updaters.py

@@ -5,14 +5,14 @@ from typing import Any, Dict
 import numpy as np
 import pytest
 from hypothesis import given, note, settings, strategies
+from xgboost.testing.params import (
+    cat_parameter_strategy,
+    exact_parameter_strategy,
+    hist_parameter_strategy,
+)
 
 import xgboost as xgb
 from xgboost import testing as tm
-from xgboost.testing.params import (
-    exact_parameter_strategy,
-    hist_parameter_strategy,
-    cat_parameter_strategy,
-)
 
 
 def train_result(param, dmat, num_rounds):