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/error-handler/ThrowableUtils.php

@@ -18,10 +18,7 @@ use Symfony\Component\ErrorHandler\Exception\SilencedErrorContext;
  */
 class ThrowableUtils
 {
-    /**
-     * @param SilencedErrorContext|\Throwable
-     */
-    public static function getSeverity($throwable): int
+    public static function getSeverity(SilencedErrorContext|\Throwable $throwable): int
     {
         if ($throwable instanceof \ErrorException || $throwable instanceof SilencedErrorContext) {
             return $throwable->getSeverity();