Fix typo bug in Index._intersection

I think this was always supposed to be checking for set membership,
not equality.

python/cudf/cudf/core/_base_index.py

@@ -1473,7 +1473,7 @@ def _intersection(self, other, sort=None):
             ._data
         )
 
-        if sort is {None, True} and len(other):
+        if sort in {None, True} and len(other):
             return intersection_result.sort_values()
         return intersection_result