[TASK] Add unit tests for PathUtility::isAbsolutePath()

Resolves: #88116
Releases: master, 9.5
Change-Id: If7e84e2c8681b8cf52d513b9520564012d8f8b73
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/60426


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Daniel Goerz <daniel.goerz@posteo.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Daniel Goerz <daniel.goerz@posteo.de>
Reviewed-by: Daniel Windloff
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>