Repro: https://codesandbox.io/s/fast-water-4i4jb

Notice the flash. I'd expect `suspended` to be `true` during the high pri render.
expect(ReactNoop.getChildren()).toEqual([span('A')]);
    
    React.unstable_withSuspenseConfig(
      () => {
        
        
        React.unstable_withSuspenseConfig(() =>
          ReactNoop.render(<App page="B" />),
        );
      },
      {timeoutMs: 2000},
    );
    expect(Scheduler).toFlushAndYield(['Suspend! [B]', 'Loading...']);
    
    expect(ReactNoop.getChildren()).toEqual([span('A')]);
    Scheduler.unstable_advanceTime(500);
    await advanceTimers(500);
    
    expect(ReactNoop.getChildren()).toEqual([
      hiddenSpan('A'),
      span('Loading...'),
    ]);
    Scheduler.unstable_advanceTime(2000);
    await advanceTimers(2000);
    expect(Scheduler).toHaveYielded(['Promise resolved [B]']);
    expect(Scheduler).toFlushAndYield(['B']);
    expect(ReactNoop.getChildren()).toEqual([span('B')]);
    React.unstable_withSuspenseConfig(
      () => {