Fixed extensionarray ref [ci skip] (#21077)

[ci skip]

Author: TomAugspurger

doc/source/whatsnew/v0.23.0.txt

@@ -202,7 +202,7 @@ for storing ip addresses.
       ...:
 
 ``IPArray`` isn't a normal 1-D NumPy array, but because it's a pandas
-:ref:`~pandas.api.extension.ExtensionArray`, it can be stored properly inside pandas' containers.
+:class:`~pandas.api.extension.ExtensionArray`, it can be stored properly inside pandas' containers.
 
 .. code-block:: ipython