[TASK] TYPO3 Coding Guidelines - TYPO3SniffPool.NamingConventions.ValidFunctionName.UnderscoresInFunctionName

Change-Id: Ief507732d53c807e5774206bb2e4bfac756f88c2
Resolves: #55034
Issues: 2.1
Reviewed-on: https://review.typo3.org/26862
Reviewed-by: Alex Kellner
Tested-by: Alex Kellner