[TASK] Must use "self::" for local static member reference

Resolves: #47926
Releases: 6.2, 6.1
Change-Id: I89aaf7e6fe75d66e3b3769c6a1b6ecd04e8b6df5
Reviewed-on: https://review.typo3.org/20502
Reviewed-by: Laurent Cherpit
Reviewed-by: Georg Ringer
Tested-by: Georg Ringer