Docs: Fix import for scikit in XGBoost template (#15693)

(cherry picked from commit 9670fa8)

docs/source-app/levels/basic/hello_components/xgboost.py

@@ -1,5 +1,5 @@
 # app.py
-# !pip install sklearn xgboost
+# !pip install scikit-learn xgboost
 import lightning as L
 from sklearn import datasets
 from sklearn.model_selection import train_test_split