[BUGFIX] Remove side effect of unit test

The class typo3/sysext/frontend/Tests/Unit/Middleware/SiteResolverTest
manipulates the locale setting of the environment without
restoring it. So following tests might get affected by this change
and are not independent anymore.

Resolves: #88484
Releases: master, 9.5
Change-Id: I02617a34bff08606866e9015111496d75bb6dcd4
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/60869


Tested-by: Benni Mack <benni@typo3.org>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>