Update VPN client to 0.21.10

[adguard-octobuddy]

A new VPN client version 0.21.10 has been released. Please integrate it.

Changelog: https://github.com/AdGuardSoftwareLimited/vpn-client/releases/tag/v0.21.10

Changelog

Fixed

• The cached backend selector config is no longer used when no backend_selector_config_fetch_urls
  are configured; the built-in defaults are used instead, as before 0.21.6. A cache written under a
  different configuration was overwriting the fallback domains supplied in
  VpnBackendClientConfig::fallback_domains (protocolConfigOverrides on Apple).