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.
span('Loading outer...'),
    ]);
    
    ReactNoop.expire(300);
    await advanceTimers(300);
    expect(Scheduler).toHaveYielded(['Promise resolved [Outer content]']);
    expect(Scheduler).toFlushAndYield([
      'Outer content',
      'Suspend! [Inner content]',
      'Loading inner...',
    ]);
    
    expect(ReactNoop.getChildren()).toEqual([
      span('Sync'),
      span('Loading outer...'),
    ]);
    
    ReactNoop.expire(500);
    await advanceTimers(500);
    
    
    expect(ReactNoop.getChildren()).toEqual([
      span('Sync'),
      span('Outer content'),
      span('Loading inner...'),
    ]);
    
    ReactNoop.expire(1000);
    await advanceTimers(1000);
    expect(Scheduler).toHaveYielded(['Promise resolved [Inner content]']);