Require isort on all Python files. (#8420)

demo/guide-python/sklearn_evals_result.py

@@ -3,10 +3,11 @@ Demo for accessing the xgboost eval metrics by using sklearn interface
 ======================================================================
 """
 
-import xgboost as xgb
 import numpy as np
 from sklearn.datasets import make_hastie_10_2
 
+import xgboost as xgb
+
 X, y = make_hastie_10_2(n_samples=2000, random_state=42)
 
 # Map labels from {-1, 1} to {0, 1}