DOC: fixup code-block directives from GH26076 (#26116)

Author: jorisvandenbossche

doc/source/whatsnew/v0.10.0.rst

@@ -430,7 +430,7 @@ Updated PyTables Support
 
 - added mixed-dtype support!
 
-   .. ipython:: python
+   .. code-block:: ipython
 
         In [64]: df['string'] = 'string'
 

doc/source/whatsnew/v0.12.0.rst

@@ -320,7 +320,7 @@ Other Enhancements
     Let's say that we had an option ``'a.b'`` and another option ``'b.c'``.
     We can set them at the same time:
 
-    .. ipython:: python
+    .. code-block:: ipython
 
         In [31]: pd.get_option('a.b')
         Out[31]: 2