[TASK] Wrong phpdoc in TableGarbageCollectionTask

The phpdoc notation of TableGarbageCollectionTask has some
pre namespaces config example.

This patch changes the phpdoc notiation.

Change-Id: Iaa0a70635893091c0ba99ce17404194c47e9a16c
Resolves: #54529
Releases: 6.2
Reviewed-on: https://review.typo3.org/26507
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn