[DOCS] Use proper "Extbase" spelling in ViewHelper

Releases: main
Resolves: #104979
Change-Id: If3a27d3f0c3cf90c53fa9d3c6eff62d6467c8321
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/86114


Reviewed-by: Garvin Hicking <gh@faktor-e.de>
Tested-by: Garvin Hicking <gh@faktor-e.de>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>