chore: Make XGB tests compatible with sklearn 1.8

PiperOrigin-RevId: 858666892

Author: sararob

tests/unit/aiplatform/test_metadata_models.py

@@ -159,6 +159,7 @@ def mock_storage_blob_download_xgboost_xgbmodel_file():
     def create_model_file(filename):
         x, y = make_classification()
         model = xgb.XGBClassifier()
+        model._estimator_type = "classifier"
         model.fit(x, y)
         model.save_model(filename)
 
@@ -522,6 +523,7 @@ def test_save_model_xgboost_xgbmodel(
 
         x, y = make_classification()
         xgb_model = xgb.XGBClassifier()
+        xgb_model._estimator_type = "classifier"
         xgb_model.fit(x, y)
 
         aiplatform.init(