fix-1535-Exception-in-the-fit()-call-of-AutoSklearn (#1539)

* Create PR

* Fix test fixture

Author: eddiebergman

test/fixtures/ensemble_building.py

@@ -231,7 +231,10 @@ def _make(
             # Hence, we take the y_train of the datamanager and use that as the
             # the targets
             if "Y_train" in datamanager.data:
-                backend.save_targets_ensemble(datamanager.data["Y_train"])
+                backend.save_additional_data(
+                    datamanager.data["Y_train"],
+                    what="targets_ensemble",
+                )
 
         return EnsembleBuilderManager(
             backend=backend,