[TASK] Avoid setMethods() in ExtractorServiceTest

Use onlyMethods() instead. Also, setAccessible()
is obsolete since PHP 8.1.

Resolves: #100422
Related: #100249
Releases: main
Change-Id: I62894d3bf19376389e14e8e2df81e0cd4324b5de
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/78393


Tested-by: Oliver Klee <typo3-coding@oliverklee.de>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Tested-by: Benni Mack <benni@typo3.org>