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/ConstraintWithRequiredArgument.php

@@ -20,7 +20,7 @@ final class ConstraintWithRequiredArgument extends Constraint
     public string $requiredArg;
 
     #[HasNamedArguments]
-    public function __construct(string $requiredArg, array $groups = null, mixed $payload = null)
+    public function __construct(string $requiredArg, ?array $groups = null, mixed $payload = null)
     {
         parent::__construct([], $groups, $payload);