Use the appropriate directive for deprecations

Author: javiereguiluz

reference/configuration/framework.rst

@@ -1172,7 +1172,7 @@ utf8
 
 **type**: ``boolean`` **default**: ``false``
 
-.. versionadded:: 5.1
+.. deprecated:: 5.1
 
     Not setting this option is deprecated since Symfony 5.1. Moreover, the
     default value of this option will change to ``true`` in Symfony 6.0.