Update requirements.txt

The current pytest error is caused by the update of scikit-learn. scikit-learn v1.6.0 has some incompatibility with xgboost, causing  error "'super' object has no attribute '__sklearn_tags__'", and the xgboost team is working on it (https://stackoverflow.com/questions/79290968/super-object-has-no-attribute-sklearn-tags).

Temporarily limit the scikit-learn version to be <1.6.

requirements.txt

@@ -5,7 +5,7 @@ matplotlib>=3.7.1
 numpy>=1.24.3, <2
 pandas>=1.5.3
 plotly>=5.9.0
-scikit_learn>=1.2.2
+scikit_learn>=1.2.2, <1.6
 # watermark>=2.3.1
 # xgboost>=1.7.6
 scipy>=1.10.1