[BUGFIX] Fix getSiteFinder() mocking in SiteProcessorTest

As it produced a warning:
1) TYPO3\CMS\Frontend\Tests\Unit\DataProcessing\SiteProcessorTest::
  nullIsProvidedIfSiteCouldNotBeRetrieved
Trying to configure method "getSiteFinder" which cannot be configured
because it does not exist, has not been specified, is final, or is static

Resolves: #88576
Related: #88568
Releases: master
Change-Id: Icf72100282ce24c87b6bb9f49fc978b6187a817e
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/61074


Tested-by: Benni Mack <benni@typo3.org>
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Benjamin Franzke <bfr@qbus.de>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Benjamin Franzke <bfr@qbus.de>