Use the FluidEmail service for sending the test task of EXT:scheduler.

Resolves: #90725
Releases: master
Change-Id: I7edb46c1e449acdb6979982c016658de95043807
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/63678


Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Benni Mack <benni@typo3.org>