Fix Sphinx warning.

Author: serhiy-storchaka

Doc/whatsnew/3.15.rst

@@ -551,7 +551,7 @@ concurrent.futures
 contextlib
 ----------
 
-* Added support for arbitrary descriptors :meth:`__enter__`,
+* Added support for arbitrary descriptors :meth:`!__enter__`,
   :meth:`!__exit__`, :meth:`!__aenter__`, and :meth:`!__aexit__` in
   :class:`~contextlib.ExitStack` and :class:`contextlib.AsyncExitStack`, for
   consistency with the :keyword:`with` and :keyword:`async with` statements.