[TASK] Do not unserialize stdClass of be_users.uc in extensionmanager

This patch changes the behaviour when saving the backendfilter in
extensionmanager list to not allow any class unserialize as TYPO3 Core
does not put any classes in the UC and no other place in Core allows
to unserialize stdClass for be_users.uc.

Resolves: #93617
Releases: master, 10.4
Change-Id: I4b0ba03fb1ea02e97327e11fcd76486d3bd4cda6
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/68155


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Benni Mack <benni@typo3.org>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>