N°6934 - Symfony 6.4 - upgrade Symfony bundles to 6.4 (#580)

* Update Symfony lib to version ~6.4.0
* Update code missing return type
* Add an iTop general configuration entry to store application secret (Symfony mandatory parameter)
* Use dependency injection in ExceptionListener & UserProvider classes

lib/symfony/config/Builder/Method.php

@@ -20,7 +20,7 @@ namespace Symfony\Component\Config\Builder;
  */
 class Method
 {
-    private $content;
+    private string $content;
 
     public function __construct(string $content)
     {