Fix flushSync warning for Combobox component with immediate prop enabled

[RobinMalfait]

This PR fixes an issue where React shows a warning that it is not able to use flushSync while it's already rendering.

The recommended solution in that case is to move the flushSync call to a scheduler task or micro task.

The scenario where it happens in this case:

{condition && (
  <Combobox immediate>
    <ComboboxInput autoFocus />
  </Combobox>
)}

This will conditionally render the Combobox with the immediate prop (which means that it will open once the ComboboxInput receives focus). But the ComboboxInput also has the autoFocus prop which means that it will focus immediately when it's rendered.

Fixes: #3334

[vercel]

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