Require isort on all Python files. (#8420)

demo/guide-python/feature_weights.py

@@ -5,11 +5,13 @@ Demo for using feature weight to change column sampling
     .. versionadded:: 1.3.0
 '''
 
-import numpy as np
-import xgboost
-from matplotlib import pyplot as plt
 import argparse
 
+import numpy as np
+from matplotlib import pyplot as plt
+
+import xgboost
+
 
 def main(args):
     rng = np.random.RandomState(1994)