9 files declare their use of ChannelInterface in Courier 8

Broken.php in src/Plugin/IdentityChannel/Broken.php

Contains \Drupal\courier\Plugin\IdentityChannel\Broken.

courier.module in ./courier.module

GlobalTemplateCollectionManager.php in src/Service/GlobalTemplateCollectionManager.php

GlobalTemplateCollectionManagerInterface.php in src/Service/GlobalTemplateCollectionManagerInterface.php

IdentityChannelPluginInterface.php in src/Plugin/IdentityChannel/IdentityChannelPluginInterface.php

Contains \Drupal\courier\Plugin\IdentityChannel\IdentityChannelPluginInterface.

MessageQueueItem.php in src/Entity/MessageQueueItem.php

TemplateCollection.php in src/Entity/TemplateCollection.php

User.php in src/Plugin/IdentityChannel/CourierEmail/User.php

Contains \Drupal\courier\Plugin\IdentityChannel\CourierEmail\User.

User.php in tests/modules/courier_test_message/src/Plugin/IdentityChannel/TestMessage/User.php