[BUGFIX] Prevent runTests.sh from removing wrong generated docs files

The directory to reference removing Documentation-GENERATED-temp
breaks out of the current working directory scope and could
possibly delete files in a completely unrelated directory. Also,
it does not remove the actual temporary files.

Resolves: #103989
Releases: main, 12.4, 11.5
Change-Id: I685a398aa0d5abee3177ab3def4e271d493d59ab
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/84464


Tested-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: core-ci <typo3@b13.com>