[TASK] UnitTests.xml cleanup

Minor cleanup in UnitTests.xml, BackupGlobals can be enabled
by default.

Resolves: #51101
Releases: 6.2

Change-Id: Ia1271d60bf29a5ac7adb98116d9d7a7a43f00b47
Reviewed-on: https://review.typo3.org/23124
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn