[BUGFIX] Add renderType to select

Add missing renderType for select box in form
flexform.

Change-Id: I58ade2720cf763cf26fc1d1e74457044ddfa054f
Resolves: #82825
Releases: master, 8.7
Reviewed-on: https://review.typo3.org/54447


Tested-by: TYPO3com <no-reply@typo3.com>
Tested-by: Riccardo De Contardi <erredeco@gmail.com>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Reviewed-by: Mathias Brodala <mbrodala@pagemachine.de>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>