[TASK] Replace prophecy in EXT:extbase BackendTest

Resolves: #98896
Releases: main
Change-Id: I3c452a229b8a690d3954cfadfa439c9b3b7be30e
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/76307


Tested-by: core-ci <typo3@b13.com>
Tested-by: Benni Mack <benni@typo3.org>
Tested-by: Oliver Klee <typo3-coding@oliverklee.de>
Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>