[TASK] Replace prophecy in EXT:core/*/UnitDeprecated/*/FileExtensionFilterTest

Resolves: #98822
Releases: main
Change-Id: I3e94df477f21600fdd0cb0eeb4ae1c9932d2bc34
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/76541


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