Guest Users can't create confidential issues anymore

Introduced in !62816 (merged) guest users were allowed to set more metadata including assignee, milestones, labels and some more.
That change has been declared as intended in #333820.

This has been change has been reverted in ec30a8d8 and is declared as a security bug in the Patch notes 14.1.2 so it looks like, this was never really intended.

However, through the revert of that change, guest users have lost the ability to create confidential issues, which can be quite critical, if they want to report security issues