[BUGFIX] Incomplete locale backup in unit test

A test from issue #43445 sets some locale categories
but does not properly reset to settings before. This
can kill unit tests running afterwards.

Change-Id: I068f0b85a5a677c5c3ae9a79b845f45d1ee9b590
Fixes: #44835
Related: #43445
Releases: 6.1, 6.0, 4.7, 4.6, 4.5
Reviewed-on: https://review.typo3.org/17735
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters
Reviewed-by: Anja Leichsenring
Tested-by: Anja Leichsenring