[BUGFIX] Set correct HTTP header when page access is denied

Accessing an existing page with insufficient permissions should
not set a 404 header but a 403 header.

Resolves: #23178
Releases: master, 8.7
Change-Id: I2470434f7600b28eaa613ee4e1669e78ceaaaec3
Reviewed-on: https://review.typo3.org/54495


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Georg Ringer <georg.ringer@gmail.com>
Tested-by: Georg Ringer <georg.ringer@gmail.com>
Reviewed-by: Susanne Moog <susanne.moog@typo3.org>
Tested-by: Susanne Moog <susanne.moog@typo3.org>