[BUGFIX] Don't render dropdown arrow in selectSingleBox

Resolves: #71750
Releases: master, 9.5
Change-Id: Ifc27ee8ed4dffba36098b9e72cac6e39cc775ebd
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/63850


Tested-by: Susanne Moog <look@susi.dev>
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Susanne Moog <look@susi.dev>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>