message: Keep GIT_ASKPASS environment variable
  This variable is used to point git towards a binary that
  implements git's credential-manager interface, and can be used
  by git to authenticate for private repositories.
  Closes Microsoft/vcpkg#23225
diff: @@ -325,6 +325,8 @@ namespace vcpkg
  // Environment variables to tell git to use custom SSH executable or command
  L"GIT_SSH",
  L"GIT_SSH_COMMAND",
  + // Points to a credential-manager binary for git authentication
  + L"GIT_ASKPASS",
  // Environment variables needed for ssh-agent based authentication
  L"SSH_AUTH_SOCK",
  L"SSH_AGENT_PID",
  