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/http-foundation/Session/Storage/MockFileSessionStorageFactory.php

@@ -21,9 +21,9 @@ class_exists(MockFileSessionStorage::class);
  */
 class MockFileSessionStorageFactory implements SessionStorageFactoryInterface
 {
-    private $savePath;
-    private $name;
-    private $metaBag;
+    private ?string $savePath;
+    private string $name;
+    private ?MetadataBag $metaBag;
 
     /**
      * @see MockFileSessionStorage constructor.