Resolve #2528166 "Upcast arg"

Closes #2528166

core/modules/rest/tests/src/Unit/CollectRoutesTest.php

@@ -88,6 +88,7 @@ protected function setUp(): void {
       ->willReturn(['basic_auth' => 'data', 'cookie' => 'data']);
 
     $container->setParameter('serializer.format_providers', ['json']);
+    $container->set('string_translation', $this->getStringTranslationStub());
 
     \Drupal::setContainer($container);