Repro case with a master build: https://codesandbox.io/s/stoic-mcnulty-dhygf?file=/src/App.js:668-703

Expected: we see content after a second.
Actual: fallback never resolves.

This happens in a sequence of:

1. Normal update
   - which suspends
2. Idle update
   - which also suspends
3. An unrelated normal update immediately followed by a ping (so they're batched)
   - here, we decide to stay on fallback, but should've shown the content

If you remove `_setVersion(v => v + 1);` on line 44 then the issue goes away.
ReactNoop.render(<App highPri="A" lowPri="1" />);
    expect(Scheduler).toFlushAndYield(['A', 'Suspend! [1]', 'Loading...']);
    await resolveText('1');
    expect(Scheduler).toHaveYielded(['Promise resolved [1]']);
    expect(Scheduler).toFlushAndYield(['A', '1']);
    expect(ReactNoop.getChildren()).toEqual([span('A'), span('1')]);
    
    ReactNoop.render(<App highPri="A" lowPri="2" />);
    expect(Scheduler).toFlushAndYield([
      'A',
      
      'Suspend! [2]',
      'Loading...',
    ]);
    
    
    ReactNoop.flushSync(() => {
      ReactNoop.render(<App highPri="B" lowPri="1" />);
    });
    expect(Scheduler).toHaveYielded(['B', '1']);
    expect(ReactNoop.getChildren()).toEqual([span('B'), span('1')]);
    
    await resolveText('2');
    expect(Scheduler).toHaveYielded(['Promise resolved [2]']);
    expect(ReactNoop.getChildren()).toEqual([span('B'), span('1')]);
  });
  it('keeps working on lower priority work after being pinged', async () => {
    
    ReactNoop.expire(149);
    function App(props) {