[CLEANUP] Review comment of PageRepository::getPage()

Note:

Type hints are not trivial to add to the signature. Although the
method always returns an array, there are unit tests that make use
of the assumption that the method is allowed to return null. Fixing
this goes beyond the goals of this ticket.

Releases: master, 8.7
Resolves: #81280
Change-Id: If47041fb6fc4835de879e9077b0359063083cbd2
Reviewed-on: https://review.typo3.org/52878


Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>