[TASK] Add additional test to YamlFileLoader

Provide an additional test to check for correct usage of numeric keys.

Resolves: #94852
Releases: main, 12.4
Change-Id: I01c73fb3e1aa0f4d458e9d349484856cb416387d
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/84957


Tested-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: core-ci <typo3@b13.com>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>