[BUGFIX] Only set a session anonymous if in FE context

The session id regeneration must not touch the sys_anonymous field
of the session record, since it only exists for FE session.
The FrontendUserAuthentication is responsible for this.

Resolves: #79757
Releases: master
Change-Id: Iefcc678b9171830b587432fa7fbbc9e77033931f
Reviewed-on: https://review.typo3.org/51635


Reviewed-by: Nicole Cordes <typo3@cordes.co>
Tested-by: Nicole Cordes <typo3@cordes.co>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Markus Klein <markus.klein@typo3.org>
Tested-by: Markus Klein <markus.klein@typo3.org>