CLN: avoid _ndarray_values in reshape.merge (pandas-dev#32693)

Author: jbrockmendel

pandas/core/reshape/merge.py

@@ -1657,10 +1657,13 @@ def _get_merge_keys(self):
     def _get_join_indexers(self):
         """ return the join indexers """
 
-        def flip(xs):
+        def flip(xs) -> np.ndarray:
             """ unlike np.transpose, this returns an array of tuples """
             xs = [
-                x if not is_extension_array_dtype(x) else x._ndarray_values for x in xs
+                x
+                if not is_extension_array_dtype(x)
+                else extract_array(x)._values_for_argsort()
+                for x in xs
             ]
             labels = list(string.ascii_lowercase[: len(xs)])
             dtypes = [x.dtype for x in xs]