bpo-39229: fix formatting in library/functions.rst (#17857)

Missing reference of auditing event presents error when building translated documentation

Author: rffontenelle

Doc/library/functions.rst

@@ -859,8 +859,8 @@ are always available.  They are listed here in alphabetical order.
 
    .. audit-event:: builtins.input/result result input
 
-      Raises an auditing event ``builtins.input/result`` with the result after
-      successfully reading input.
+      Raises an :ref:`auditing event <auditing>` ``builtins.input/result``
+      with the result after successfully reading input.
 
 
 .. class:: int([x])