[BUGFIX] Container registration of ext:fluid_test VH's

Viewhelpers need to be registered in Services.yaml.
Add this for a functional test related fixture extension.

Resolves: #95521
Releases: master
Change-Id: I27f56c89958d4338c2d7f8bdd3c0c8defceb7da8
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/71482


Tested-by: core-ci <typo3@b13.com>
Tested-by: Jochen <rothjochen@gmail.com>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Jochen <rothjochen@gmail.com>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>