[DOCS] Fix typoscript example in EXT:form

Indentation and closing braces are fixed.

Releases: master, 10.4
Resolves: #92453
Change-Id: I6a6cc74a9d60a358f13c71e3bc8cddaf91ab77ee
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/65966


Tested-by: Oliver Bartsch <bo@cedev.de>
Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Daniel Goerz <daniel.goerz@posteo.de>
Reviewed-by: Oliver Bartsch <bo@cedev.de>
Reviewed-by: Daniel Goerz <daniel.goerz@posteo.de>