Update VPN client to 0.21.12

[adguard-octobuddy]

A new VPN client version 0.21.12 has been released. Please integrate it.

Changelog: https://github.com/AdGuardSoftwareLimited/vpn-client/releases/tag/v0.21.12

Changelog

Changed

• Android: the device token long poll can be cancelled with AuthApi.grantDeviceTokenPoll(String, CancellationSignal),
  which replaces grantDeviceTokenPoll(String).
  Cancelling the signal aborts the request in flight and throws android.os.OperationCanceledException.