[TASK] Align some testing details with recent TF works

* TYPO3_TESTING_FUNCTIONAL_REMOVE_ERROR_HANDLER is
  obsolete
* phpunit 9.5 is minimum requirement
* An acceptance test setup detail has been activated
  in testing-framework by default

Change-Id: Idaafa923fe8544fdd9f20395de6557be709562cb
Resolves: #96106
Releases: master
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/72329


Tested-by: core-ci <typo3@b13.com>
Tested-by: Stefan Bürk <stefan@buerk.tech>
Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Stefan Bürk <stefan@buerk.tech>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>