Avoid error lexing multiprocessing docs code block on Pygments 2.15.0

Author: CAM-Gerlach

Doc/library/multiprocessing.rst

@@ -452,7 +452,9 @@ process which created it.
    importable by the children. This is covered in :ref:`multiprocessing-programming`
    however it is worth pointing out here. This means that some examples, such
    as the :class:`multiprocessing.pool.Pool` examples will not work in the
-   interactive interpreter. For example::
+   interactive interpreter. For example:
+
+   .. code-block:: text
 
       >>> from multiprocessing import Pool
       >>> p = Pool(5)