[BUGFIX] Failing test in VersionNumberUtility

The core update patch changed a method in VersionNumberUtility
from protected to public but did not adapt a test that relied
on this. This is fixed with the patch together with a minor cleanup.

Change-Id: I17b1e9e9ba5f3f15ca0483ccf0b1132e26cb27e7
Resolves: #52608
Releases: 6.2
Reviewed-on: https://review.typo3.org/24487
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn