Merge branch '6.4' into 7.0

* 6.4: (24 commits)
  Fix Twig tests
  [Scheduler] Fix tests
  [TwigBridge] Add FormLayoutTestCase class
  Fix CS
  Allow sending scheduled messages through the slack API
  [TwigBridge] Add `AppVariable::getEnabledLocales()` to retrieve the enabled locales
  [RateLimiter] Add missing dependency
  [RateLimiter] Add SlidingWindowLimiter::reserve()
  [Messenger] Add WrappedExceptionsInterface for nested exceptions
  [Mime] Add `TemplatedEmail::locale()` to set the locale for the email rendering
  Fix CS
  [Messenger][Scheduler] Add AsCronTask & AsPeriodicTask attributes
  [Scheduler] Make debug:scheduler output more useful
  [Notifier] Tweak some phpdocs
  [FrameworkBundle] Change BrowserKitAssertionsTrait::getClient() to be protected
  Fix CS
  [FrameworkBundle] Allow BrowserKit relative URL redirect assert
  [Messenger] RejectRedeliveredMessageException should not be retried
  [Serializer] Make `ProblemNormalizer` give details about Messenger’s `ValidationFailedException`
  [WebProfilerBundle] Support `!` negation operator in url filter
  ...

Author: fabpot

Mailer.php

@@ -65,7 +65,7 @@ public function send(RawMessage $message, Envelope $envelope = null): void
         try {
             $this->bus->dispatch(new SendEmailMessage($message, $envelope), $stamps);
         } catch (HandlerFailedException $e) {
-            foreach ($e->getNestedExceptions() as $nested) {
+            foreach ($e->getWrappedExceptions() as $nested) {
                 if ($nested instanceof TransportExceptionInterface) {
                     throw $nested;
                 }