Address review: fix run_model_on_task example, remove unwanted files

- Use HistGradientBoostingClassifier instead of DecisionTreeClassifier
  (fixes ValueError with missing values in task 1)
- Remove .DS_Store
- Remove tests/files/misc/features_with_whitespaces.xml.pkl

Author: Abhishek

.DS_Store

@@ -109,8 +109,8 @@ def run_model_on_task(  # noqa: PLR0913
     --------
     >>> import openml
     >>> import openml_sklearn  # doctest: +SKIP
-    >>> from sklearn.tree import DecisionTreeClassifier  # doctest: +SKIP
-    >>> clf = DecisionTreeClassifier()  # doctest: +SKIP
+    >>> from sklearn.ensemble import HistGradientBoostingClassifier  # doctest: +SKIP
+    >>> clf = HistGradientBoostingClassifier()  # doctest: +SKIP
     >>> task = openml.tasks.get_task(1)  # doctest: +SKIP
     >>> run = openml.runs.run_model_on_task(clf, task)  # doctest: +SKIP
     """