[BUGFIX] Avoid SQL error for scheduler task on PostgreSQL

This patch makes sure tx_scheduler_task.task_group contains an integer
in order to avoid a SQL error when saving the task which in turn may
lead to an endless fetch-and-save loop.

Resolves: #94102
Releases: master, 10.4
Change-Id: Ie81d2c3a7eb193f4fd1ed59c34fe2de9fad023f4
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/69097


Tested-by: core-ci <typo3@b13.com>
Tested-by: Simon Gilli <typo3@gilbertsoft.org>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Simon Gilli <typo3@gilbertsoft.org>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Guido Schmechel <guido.schmechel@brandung.de>
Reviewed-by: Daniel Goerz <daniel.goerz@posteo.de>
Reviewed-by: Benni Mack <benni@typo3.org>