[Service Container] Fix typo in tag default index method name

Author: nemoipaha

service_container/tags.rst

@@ -807,7 +807,7 @@ array element. For example, to retrieve the ``handler_two`` handler::
 .. tip::
 
  Just like the priority, you can also implement a static
- ``getDefaultIndexAttributeName()`` method in the handlers and omit the
+ ``getDefaultIndexName()`` method in the handlers and omit the
  index attribute (``key``)::
 
  // src/Handler/One.php