Merge branch '6.4' into 7.0

* 6.4:
  stop marking parameters implicitly as nullable
  include message id provided by the MTA when dispatching the SentMessageEvent

Tests/Fixtures/TranslatableTextAlign.php

@@ -20,7 +20,7 @@ enum TranslatableTextAlign implements TranslatableInterface
     case Center;
     case Right;
 
-    public function trans(TranslatorInterface $translator, string $locale = null): string
+    public function trans(TranslatorInterface $translator, ?string $locale = null): string
     {
         return $translator->trans($this->name, locale: $locale);
     }