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/dependency-injection/Variable.php

@@ -26,17 +26,14 @@ namespace Symfony\Component\DependencyInjection;
  */
 class Variable
 {
-    private $name;
+    private string $name;
 
     public function __construct(string $name)
     {
         $this->name = $name;
     }
 
-    /**
-     * @return string
-     */
-    public function __toString()
+    public function __toString(): string
     {
         return $this->name;
     }