Use black on more Python files. (#8137)

demo/guide-python/categorical.py

@@ -16,11 +16,13 @@ categorical data.
     .. versionadded:: 1.5.0
 
 """
-import pandas as pd
-import numpy as np
-import xgboost as xgb
 from typing import Tuple
 
+import numpy as np
+import pandas as pd
+
+import xgboost as xgb
+
 
 def make_categorical(
     n_samples: int, n_features: int, n_categories: int, onehot: bool