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/cache/Marshaller/MarshallerInterface.php

@@ -32,9 +32,7 @@ interface MarshallerInterface
     /**
      * Unserializes a single value and throws an exception if anything goes wrong.
      *
-     * @return mixed
-     *
      * @throws \Exception Whenever unserialization fails
      */
-    public function unmarshall(string $value);
+    public function unmarshall(string $value): mixed;
 }