title: fullcalendar v5 useref() in react does not contain calendar
body: <p>I am using react version of fullcalendar and this is a part of my component:</p>
  <pre><code>const itMaker = React.useRef();
  ...
  &lt;FullCalendar
    ref={itMaker}
    ...
    customButtons={{
      prev: {
        click: function () {
          console.log('itMaker', itMaker)
          itMaker.current.calendar.incrementDate({ days: -1 });
        }
      }
    }}
  </code></pre>
  <p><code>useref()</code> result is different in v4 and v5. The result in v4 is the same as bellow:</p>
  <p><img src="https://i.imgur.com/DhMdYp3.jpg" alt="Imgur" /></p>
  <p>❌ And this is the result of <code>useref()</code> in fullcalendar v5:</p>
  <p><img src="https://i.imgur.com/TgFq98O.jpg" alt="Imgur" /></p>
  <p>The problem is that <code>calendar</code> exists in <code>useref()</code> in v4 but not in v5!!</p>