[BUGFIX] Use interface SiteInterface as return type instead of Site

To avoid exceptions the proper return type must be used.

Resolves: #86390
Releases: master
Change-Id: I3741582936cb1e1b530012a1c7fb8ff3ab6da934
Reviewed-on: https://review.typo3.org/58403


Reviewed-by: Tymoteusz Motylewski <t.motylewski@gmail.com>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Susanne Moog <susanne.moog@typo3.org>
Tested-by: Susanne Moog <susanne.moog@typo3.org>