[TASK] Move ExceptionHandler tests into real class instances

The accessibleMockForAbstractClasses is a discouraged concept
anyways, and in this case the constructor definition in the
interface caused a test failure.
Moving the tests to concrete classes solves the failure and
also gets rid of the abstract class mock.

Resolves: #90942
Releases: master, 9.5
Change-Id: I902cabd3290761c1525b128eb18822199f337cb5
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/64066


Tested-by: Alexander Schnitzler <git@alexanderschnitzler.de>
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Andreas Fernandez <a.fernandez@scripting-base.de>
Reviewed-by: Alexander Schnitzler <git@alexanderschnitzler.de>
Reviewed-by: Andreas Fernandez <a.fernandez@scripting-base.de>