fixup! add serializer test

Author: blizzz

tests/lib/Log/ExceptionSerializerTest.php

@@ -31,7 +31,7 @@
 use Test\TestCase;
 
 class ExceptionSerializerTest extends TestCase {
-	private ExceptionSerializer $serializer;
+	private $serializer;
 
 	public function setUp(): void {
 		parent::setUp();