[BUGFIX] Use appropriate icon for "New group" button

Resolves: #100253
Related: #99874
Releases: main
Change-Id: Ib01e654e3f1e36a1168aab36fb4429f1c324e9d8
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/78212


Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Benni Mack <benni@typo3.org>