6 files declare their use of QueueWorkerBase

AggregatorRefresh.php in core/modules/aggregator/src/Plugin/QueueWorker/AggregatorRefresh.php
CronQueueTestBrokenQueue.php in core/modules/system/tests/modules/cron_queue_test/src/Plugin/QueueWorker/CronQueueTestBrokenQueue.php
CronQueueTestException.php in core/modules/system/tests/modules/cron_queue_test/src/Plugin/QueueWorker/CronQueueTestException.php
CronQueueTestRequeueException.php in core/modules/system/tests/modules/cron_queue_test/src/Plugin/QueueWorker/CronQueueTestRequeueException.php
LocaleTranslation.php in core/modules/locale/src/Plugin/QueueWorker/LocaleTranslation.php
ThumbnailDownloader.php in core/modules/media/src/Plugin/QueueWorker/ThumbnailDownloader.php

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