Update security.rst

Fixing backticks https://github.com/symfony/symfony-docs/pull/13414/files#r397825547

Author: ThomasLandauer

reference/configuration/security.rst

@@ -68,8 +68,8 @@ anonymous
 **type**: ``string`` **default**: ``~``
 
 When set to ``lazy``, Symfony loads the user (and starts the session) only if the
-application actually accesses the `User` object (e.g. via a `is_granted()` call in
-a template or `isGranted()` in a controller or service.
+application actually accesses the ``User`` object (e.g. via a ``is_granted()`` call
+in a template or ``isGranted()`` in a controller or service.
 
 .. versionadded:: 4.4