FreeScout: a restricted agent can lift their own admin-imposed "see only assigned conversations" restriction via profile save

FreeScout is a self-hosted help desk and shared mailbox. Prior to 1.8.231, the profile form exposes the only_assigned_tickets permission to its non-admin owner, and UsersController::profileSave() adds or removes User::PERM_ONLY_ASSIGNED_TICKETS without checking that the editor is an administrator. A restricted agent can uncheck the option, or submit an ordinary profile save that omits it, to remove the administrator-imposed restriction. The agent can then read and modify conversations assigned to other agents in every mailbox they already belong to. This issue is fixed in version 1.8.231.