CLN: Use exclusions in determination of _selected_obj (#50416)

Author: rhshadrach

pandas/core/groupby/groupby.py

@@ -1021,7 +1021,7 @@ def _set_group_selection(self) -> None:
         ):
             return
 
-        groupers = [g.name for g in grp.groupings if g.level is None and g.in_axis]
+        groupers = self.exclusions
 
         if len(groupers):
             # GH12839 clear selected obj cache when group selection changes