[TASK] Refactor scheduler task acceptance tests

* Use Admin Actor
* Rename the class / test
* Split the test in smaller pieces
* Make the test more robust
* Add test for deleting a scheduler task

Change-Id: I0b1c0e326bc27590311451fd46cb40600af30719
Resolves: #75618
Releases: master
Reviewed-on: https://review.typo3.org/47667


Reviewed-by: Dirk Jüttner <dirk.juettner@gmail.com>
Tested-by: Dirk Jüttner <dirk.juettner@gmail.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>