[TASK] Avoid state and undefined properties in tests

There is often no point in having test class state
which may lead to undefined class properties and
more complex test setups.

The patch simplifies a test to show this is more
easy to grasp and solve a phpstan error along the way.

> Build/Scripts/runTests.sh -s phpstanGenerateBaseline

Resolves: #96685
Releases: main, 11.5
Change-Id: I271fa1b71d9ac234249c786af14da4e72a03ee7c
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/73214


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