React version: 18.3.0-next-3ba7add60-20221201

Hard to reproduce.

In Next.js, in rare cases, and only after a fast refresh, the ref object when using forwardRef is simply `{}`.

This leads to the `TypeError: can't define property "current": Object is not extensible` error when used with `useImperativeHandle`.

```tsx
function Parent() {
  const carouselRef = useRef<any>();

  return <Suspense><Carousel ref={carouselRef} /></Suspense>
}

const Carousel = forwardRef((props, ref) => {
  if (!('current' in ref)) { debugger; }
  const thing = use(aPromise);
  return ...;
});
```

![Screenshot 2023-03-17 at 18 49 21](https://user-images.githubusercontent.com/5406212/225981809-22f575fa-0ec7-4f94-ae23-bffc8bf7c4dd.png)

In `updateImperativeHandle`, the ref is already an empty object.

![Screenshot 2023-03-17 at 19 13 13](https://user-images.githubusercontent.com/5406212/225985622-b8512a61-3a6b-4958-b63f-277219d4c816.png)

I haven't investigated it further yet, the stacktraces are quite hard to follow.
resetRenderTimer();
    }
  }
}
 Overload the definition to the two valid signatures.
 Warning, this opts-out of checking the function body.
 eslint-disable-next-line no-unused-vars
declare function flushSync<R>(fn: () => R): R;
 eslint-disable-next-line no-redeclare
declare function flushSync(void): void;
 eslint-disable-next-line no-redeclare
export function flushSync<R>(fn: (() => R) | void): R | void {
   
   
  if (
    rootWithPendingPassiveEffects !== null &&
    rootWithPendingPassiveEffects.tag === LegacyRoot &&
    (executionContext & (RenderContext | CommitContext)) === NoContext
  ) {
    flushPassiveEffects();
  }
  const prevExecutionContext = executionContext;
  executionContext |= BatchedContext;
  const prevTransition = ReactCurrentBatchConfig.transition;
  const previousPriority = getCurrentUpdatePriority();
  try {
    ReactCurrentBatchConfig.transition = null;
    setCurrentUpdatePriority(DiscreteEventPriority);
    if (fn) {
      return fn();