[TASK] Tests: Do not initialize TYPO3_DB in unit tests

Change-Id: I9d147353411314416cdf1f5196d18a127e8c5145
Resolves: #56948
Related: #51436
Releases: 6.2
Reviewed-on: https://review.typo3.org/28432
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn