[TASK] Replace prophecy in EXT:form FormFrontendControllerTest

Resolves: #98978
Releases: main
Change-Id: I1bf664b460c2a9e820382e009caefee5cdc5472f
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/76825


Tested-by: core-ci <typo3@b13.com>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Oliver Klee <typo3-coding@oliverklee.de>
Reviewed-by: Nikita Hovratov <nikita.h@live.de>
Reviewed-by: Oliver Klee <typo3-coding@oliverklee.de>
Tested-by: Nikita Hovratov <nikita.h@live.de>