[TASK] Have static DP in BrokenLinkRepositoryTest

Clean up and simplify a bit along the way.

Resolves: #100450
Related: #100249
Releases: main
Change-Id: I0f808487226689a701e9224c1e93daf2f2fbd7ae
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/78464


Tested-by: core-ci <typo3@b13.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Stefan Bürk <stefan@buerk.tech>