Adding flag android.security.secure_lockdown to trunk_staging.

This change was automatically created by advancing the Gantry workflow at:
https://releasetracker.partner.android.com/changes/chl3vvi000001?build_unique_id=AndroidSecuritySecureLockdownLaunch-platform
Do not edit this file manually or revert this change - use the Gantry workflow to manage the state of this flag.

Bug: 373422357
Change-Id: Ibaf5c5cf4e3ebae565c1a5bdae5b81751cac9e43
Flag: android.security.secure_lockdown
Ignore-AOSP-First: AConfig change for future AOSP release