[BUGFIX] Make parallel execution checkbox in scheduler working

The markup is adjusted to make the "parallel
execution" checkbox in the scheduler module
edit view working again.

Additionally, the checkbox is only displayed
for recuring tasks, because it's always set
to FALSE for tasks with single execution.

Resolves: #101146
Releases: main, 12.4
Change-Id: I0bc595683565ab099ca2a78f7a0aaf1480255a8f
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/79674


Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Oliver Bartsch <bo@cedev.de>