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-kernel/Fragment/SsiFragmentRenderer.php

@@ -18,10 +18,7 @@ namespace Symfony\Component\HttpKernel\Fragment;
  */
 class SsiFragmentRenderer extends AbstractSurrogateFragmentRenderer
 {
-    /**
-     * {@inheritdoc}
-     */
-    public function getName()
+    public function getName(): string
     {
         return 'ssi';
     }