review: add versionadded directive

Author: bpolaszek

configuration/env_var_processors.rst

@@ -137,6 +137,11 @@ Symfony provides the following env var processors:
             ]);
 
 ``env(not:FOO)``
+
+    .. versionadded:: 5.3
+
+        The ``not:`` env var processor was introduced in Symfony 5.3.
+
     Casts ``FOO`` to a bool (just as ``env(bool:...)`` does) except it returns the inverted value
     (falsy values are returned as ``true``, truthy values are returned as ``false``):