update whatsnew code display

Author: Jiang Yue

doc/source/whatsnew/v0.25.0.rst

@@ -97,18 +97,18 @@ would be reassigned as -1. (:issue:`19387`)
 
 .. code-block:: ipython
 
-    MultiIndex(levels=[[nan, None, NaT, 128, 2]],
-               codes=[[0, -1, 1, 2, 3, 4]])
-    MultiIndex(levels=[[1, 2]],
-               codes=[[0, -2]])
+    Out[1]: MultiIndex(levels=[[nan, None, NaT, 128, 2]],
+                       codes=[[0, -1, 1, 2, 3, 4]])
+    Out[2]: MultiIndex(levels=[[1, 2]],
+                       codes=[[0, -2]])
 
 *New Behavior*:
 
-.. ipython:: python
+.. ipython:: ipython
 
-    MultiIndex(levels=[[nan, None, NaT, 128, 2]],
+    Out[1]: MultiIndex(levels=[[nan, None, NaT, 128, 2]],
                codes=[[-1, -1, -1, -1, 3, 4]])
-    ValueError: On level 0, code value (-2) < -1
+    Out[2]: ValueError: On level 0, code value (-2) < -1
 
 
 .. _whatsnew_0250.api_breaking.groupby_apply_first_group_once: