EventSubscriber/RedirectResponseSubscriberTest must not use the Symfony EventDispatcher but Drupal's

Problem/Motivation

As a pre-requisite of #2876675: Allow symfony/event-dispatcher 4+ to be installed in Drupal 8 any maybe other issues like #3020303: Consider using Symfony flex to allow switching between major Symfony versions, we need to change the EventSubscriber/RedirectResponseSubscriberTest.

Instead of using using the Symfony\Component\EventDispatcher\EventDispatcher which would change in an incompatible way in Symfony >= 4.3 we must use our own Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher as EventDispatcher;

Proposed resolution

Adjust the test.

Remaining tasks

Commit the patch.

User interface changes

none

API changes

none

Data model changes

none

Release notes snippet

none