Fix phpcs

src/Mailer/Message.php

@@ -304,7 +304,7 @@ class Message implements JsonSerializable
      *
      * @var array<string>
      */
-    protected $serializableProperties = [
+    protected array $serializableProperties = [
         'to', 'from', 'sender', 'replyTo', 'cc', 'bcc', 'subject',
         'returnPath', 'readReceipt', 'emailFormat', 'emailPattern', 'domain',
         'attachments', 'messageId', 'headers', 'appCharset', 'charset', 'headerCharset',

tests/TestCase/Mailer/MessageTest.php

@@ -22,6 +22,7 @@ use Cake\Mailer\Transport\DebugTransport;
 use Cake\TestSuite\TestCase;
 use InvalidArgumentException;
 use Laminas\Diactoros\UploadedFile;
+use ReflectionClass;
 use TestApp\Mailer\TestMessage;
 
 /**
@@ -1306,7 +1307,7 @@ HTML;
     public function testSerialization(): void
     {
         $message = new Message();
-        $reflection = new \ReflectionClass($message);
+        $reflection = new ReflectionClass($message);
         $property = $reflection->getProperty('serializableProperties');
         $property->setAccessible(true);
         $serializableProperties = $property->getValue($message);