As described in https://github.com/electron/electron/pull/13769, we had to disable mixed sandbox related tests for Windows CI. We should re-enable them back after finding out the root reason.
atom/app/atom_main_delegate.cc
utility_client_.reset(new AtomContentUtilityClient);
  return utility_client_.get();
}
int AtomMainDelegate::RunProcess(
    const std::string& process_type,
    const content::MainFunctionParams& main_function_params) {
  if (process_type == kRelauncherProcess)
    return relauncher::RelauncherMain(main_function_params);
  else
    return -1;
}
#if defined(OS_MACOSX)
bool AtomMainDelegate::ShouldSendMachPort(const std::string& process_type) {
  return process_type != kRelauncherProcess;
}
bool AtomMainDelegate::DelaySandboxInitialization(
    const std::string& process_type) {
  return process_type == kRelauncherProcess;
}
#endif
bool AtomMainDelegate::ShouldLockSchemeRegistry() {
  return false;
}
bool AtomMainDelegate::ShouldCreateFeatureList() {
  return false;
}
}