6 files declare their use of CacheableJsonResponse in Drupal 9

ExceptionHandlingTest.php in core/tests/Drupal/KernelTests/Core/Routing/ExceptionHandlingTest.php

ExceptionJsonSubscriber.php in core/lib/Drupal/Core/EventSubscriber/ExceptionJsonSubscriber.php

ExceptionJsonSubscriberTest.php in core/tests/Drupal/Tests/Core/EventSubscriber/ExceptionJsonSubscriberTest.php

JsonRenderer.php in core/modules/system/tests/modules/common_test/src/Render/MainContent/JsonRenderer.php

PageCacheAcceptHeaderController.php in core/modules/system/tests/modules/system_test/src/Controller/PageCacheAcceptHeaderController.php

QuickEditImageController.php in core/modules/image/src/Controller/QuickEditImageController.php