[BUGFIX] Add margin-bottom for tab-content

This adds a margin between the tab-content and the submit-button in the
extension configuration form.

Resolves: #86562
Releases: master
Change-Id: Ifdbf30af3cb92162c876c49b46d32776b654991e
Reviewed-on: https://review.typo3.org/58572


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Susanne Moog <susanne.moog@typo3.org>
Tested-by: Susanne Moog <susanne.moog@typo3.org>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>