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/polyfill-intl-grapheme/Grapheme.php

@@ -48,7 +48,7 @@ final class Grapheme
             $start = \strlen($s) + $start;
         }
 
-        if (!is_scalar($s)) {
+        if (!\is_scalar($s)) {
             $hasError = false;
             set_error_handler(function () use (&$hasError) { $hasError = true; });
             $next = substr($s, $start);