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/var-dumper/Caster/ProxyManagerCaster.php

@@ -21,6 +21,9 @@ use Symfony\Component\VarDumper\Cloner\Stub;
  */
 class ProxyManagerCaster
 {
+    /**
+     * @return array
+     */
     public static function castProxy(ProxyInterface $c, array $a, Stub $stub, bool $isNested)
     {
         if ($parent = get_parent_class($c)) {