9 files declare their use of PostResponseEvent in Zircon Profile 8

AutomatedCron.php in core/modules/automated_cron/src/EventSubscriber/AutomatedCron.php

Contains \Drupal\automated_cron\EventSubscriber\AutomatedCron.

HttpKernel.php in vendor/symfony/http-kernel/HttpKernel.php

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

Contains \Drupal\Core\EventSubscriber\KernelDestructionSubscriber.

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

Contains \Drupal\Core\EventSubscriber\PathSubscriber.

ProfilerListener.php in vendor/symfony/http-kernel/EventListener/ProfilerListener.php

ProfilerListenerTest.php in vendor/symfony/http-kernel/Tests/EventListener/ProfilerListenerTest.php

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

Contains \Drupal\Core\EventSubscriber\RequestCloseSubscriber.

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

Contains \Drupal\Core\EventSubscriber\RouterRebuildSubscriber.

UserRequestSubscriber.php in core/modules/user/src/EventSubscriber/UserRequestSubscriber.php

Contains \Drupal\user\EventSubscriber\UserRequestSubscriber.