Replace :class: with :data: for DefaultContext, BasicContext, and ExtendedContext in documentation

Author: abkmystery

Doc/whatsnew/3.3.rst

@@ -1147,8 +1147,8 @@ API changes
    | :const:`MIN_EMIN` | ``-425000000`` | ``-999999999999999999`` |
    +-------------------+----------------+-------------------------+
 
-* In the context templates (:class:`~decimal.DefaultContext`,
-  :class:`~decimal.BasicContext` and :class:`~decimal.ExtendedContext`)
+* In the context templates (:data:`~decimal.DefaultContext`,
+  :data:`~decimal.BasicContext` and :data:`~decimal.ExtendedContext`)
   the magnitude of :attr:`~decimal.Context.Emax` and
   :attr:`~decimal.Context.Emin` has changed to ``999999``.