[TASK] Improve PHPunit used assertions

Main changes are:

* Use assertArrayHasKey/assertArrayNotHasKey instead of array_key_exists.
* Fix misordered assertEquals/assertNotEquals arguments.
* Use assertCount instead of assertEquals and count() method.

Resolves: #94751
Releases: master
Change-Id: Iaa0dbb4744bf41f43f4700714ed47910feaab081
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/70292


Tested-by: core-ci <typo3@b13.com>
Tested-by: Roman Büchler <info@buechler.pro>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Roman Büchler <info@buechler.pro>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>