chore: document latest LTS

https://symfony.com/versions.json

setup.rst

@@ -272,14 +272,14 @@ stable version. If you want to use an LTS version, add the ``--version`` option:
  $ symfony new my_project_directory --version=next
 
  # you can also select an exact specific Symfony version
- $ symfony new my_project_directory --version="5.4.*"
+ $ symfony new my_project_directory --version="6.4.*"
 
 The ``lts`` and ``next`` shortcuts are only available when using Symfony to
 create new projects. If you use Composer, you need to tell the exact version:
 
 .. code-block:: terminal
 
- $ composer create-project symfony/skeleton:"5.4.*" my_project_directory
+ $ composer create-project symfony/skeleton:"6.4.*" my_project_directory
 
 The Symfony Demo application
 ----------------------------