[TASK] Rename Acceptance test suite from Backend to Application

Now that we have frontend tests in the Backend suite the
name Backend for acceptance suite does not fit anymore.

So the suite name was changed from Backend to Application.

Resolves: #94864
Releases: master
Change-Id: Ib52053f6dbbfad9b7fef1ff11e81110cffa010b2
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/70550


Tested-by: core-ci <typo3@b13.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>