Merge branch '6.4' into 7.0

* 6.4:
  [Mime] Fix lowest versions of deps
  [VarDumper] Fix calling scope detection inside magic accessors
  [Validator] add missing German translations
  fix deprecation versions
  update the Brevo SMTP host
  Remove \ReflectionProperty::setAccessible(true) calls
  [Serializer] Fix denormalizing abstract part headers in MimeMessageNormalizer
  Fix property must not be accessed before initialization on SymfonyRuntime::$input
  [Form] Remove an obsolete phpdoc comment
  [Webhook] Allow slash in webhook type
  Use more "First class callable syntax" + Normalize set_error_handler/set_exception_handler calls
  [FrameworkBundle][Workflow] Throw exception is workflow.xxx.transitions is not an array

Author: nicolas-grekas

Debug/TraceableEventDispatcher.php

@@ -329,7 +329,6 @@ private function getListenersWithPriority(): array
         $result = [];
 
         $allListeners = new \ReflectionProperty(EventDispatcher::class, 'listeners');
-        $allListeners->setAccessible(true);
 
         foreach ($allListeners->getValue($this->dispatcher) as $eventName => $listenersByPriority) {
             foreach ($listenersByPriority as $priority => $listeners) {