[TASK] Make FileBackendTest a functional test

Moving cache framework related FileBackendTest
unit tests to functional tests needs less mocks
and avoids vfsStream.

> Build/Scripts/runTests.sh -s phpstanGenerateBaseline

Resolves: #98931
Resolves: #98734
Releases: main
Change-Id: I0090ae0c0984add6584f3858df35fed5df91ab91
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/76295


Tested-by: core-ci <typo3@b13.com>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>