Spin group wait causes ClosedQueueError

After updating to 2.2.3 to 2.3.0, waiting in a spingroup seems to have broken and now throws a ClosedQueueError.

Minimal test case:

require 'cli/ui'

CLI::UI::StdoutRouter.enable

CLI::UI::SpinGroup.new do |sg|
  # Task 1
  sg.add('pending') { |spinner|
    result = { 'message' => 'mock api result' }
    sleep(0.5)
    spinner.update_title(result['message'])
  }

  # Wait for previous task to finish before starting the next
  sg.wait

  # Task 2
  sg.add('pending 2') { |spinner|
    result = { 'message' => 'mock api result 2' }
    sleep(0.5)
    spinner.update_title(result['message'])
  }
end

Full output:

# ruby test.rb
✓ mock api result
/usr/local/bundle/gems/cli-ui-2.3.0/lib/cli/ui/work_queue.rb:86:in `push': queue closed (ClosedQueueError)
        from /usr/local/bundle/gems/cli-ui-2.3.0/lib/cli/ui/work_queue.rb:86:in `enqueue'
        from /usr/local/bundle/gems/cli-ui-2.3.0/lib/cli/ui/spinner/spin_group.rb:135:in `initialize'
        from /usr/local/bundle/gems/cli-ui-2.3.0/lib/cli/ui/spinner/spin_group.rb:315:in `new'
        from /usr/local/bundle/gems/cli-ui-2.3.0/lib/cli/ui/spinner/spin_group.rb:315:in `block in add'
        from /usr/local/bundle/gems/cli-ui-2.3.0/lib/cli/ui/spinner/spin_group.rb:314:in `synchronize'
        from /usr/local/bundle/gems/cli-ui-2.3.0/lib/cli/ui/spinner/spin_group.rb:314:in `add'
        from test.rb:17:in `block in <main>'
        from /usr/local/bundle/gems/cli-ui-2.3.0/lib/cli/ui/spinner/spin_group.rb:93:in `initialize'
        from test.rb:5:in `new'
        from test.rb:5:in `<main>'

Reproduce the regression with test.rb using the minimal SpinGroup example, then inspect lib/cli/ui/work_queue.rb:86 and lib/cli/ui/spinner/spin_group.rb:135, 314-315. Trace why sg.wait closes the queue before the second sg.add enqueues work; done when the example completes both tasks without ClosedQueueError and a regression test covers it.