Tests: fix for PHP 8.4 deprecation of implicitly nullable types

This will work for now. PHPCS 4.0 will remove the whole outdated TestSuite setup as per 25, so by that time, the problem is gone completely.

Ref: https://wiki.php.net/rfc/deprecate-implicitly-nullable-types

Author: jrfnl

tests/TestSuite.php

@@ -23,7 +23,7 @@ class TestSuite extends PHPUnit_TestSuite
      *
      * @return \PHPUnit\Framework\TestResult
      */
-    public function run(TestResult $result=null): TestResult
+    public function run(?TestResult $result=null): TestResult
     {
         $result = parent::run($result);
         printPHPCodeSnifferTestOutput();