MQE-1582: Enable Testers To Run Skipped Tests

- Fix nullable type hinting

Author: KevinBKozan

src/Magento/FunctionalTestingFramework/Console/GenerateTestsCommand.php

@@ -123,7 +123,7 @@ protected function execute(InputInterface $input, OutputInterface $output)
      * @throws \Magento\FunctionalTestingFramework\Exceptions\XmlException
      */
     private function createTestConfiguration(
-        string $json,
+        $json,
         array $tests,
         bool $force,
         string $debug,