Update VPN client to 0.21.7

[adguard-octobuddy]

A new VPN client version 0.21.7 has been released. Please integrate it.

Changelog: https://github.com/AdGuardSoftwareLimited/vpn-client/releases/tag/v0.21.7

Changelog

Added

• Added ownership-tracked platform tunnel lifecycle handling so native connections fail closed when no safe outbound route is available while any tunnel is active.
• [Android] Added VpnCore.acquireTunnelActivity() / VpnCore.releaseTunnelActivity(long) for tracking the platform VPN tunnel lifecycle.

Removed

• [Apple] Removed the AGVpnCore.tunnelRunning property; tunnel activity is now tracked internally by the framework and exposed through socket protection fail-closed behavior.