fix failed cicd

Author: joyahuang

pandas/plotting/_matplotlib/boxplot.py

@@ -212,8 +212,6 @@ def _make_plot(self, fig: Figure) -> None:
 
                     # When `by` is assigned, the ticklabels will become unique grouped
                     # values, instead of label which is used as subtitle in this case.
-                    # error: "Index" has no attribute "levels"; maybe "nlevels"?
-                    levels = self.data.columns.levels  # type: ignore[attr-defined]
                     ticklabels = [pprint_thing(col) for col in self.data.columns.get_level_values(0)] # 
                 else:
                     ticklabels = [pprint_thing(label)]