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.
await advanceTimers(50);
    
    expect(Scheduler).toFlushWithoutYielding();
    expect(ReactNoop.getChildren()).toEqual([]);
    
    await advanceTimers(50);
    
    expect(Scheduler).toHaveYielded(['Promise resolved [A]']);
    expect(Scheduler).toFlushAndYield(['Foo', 'Bar', 'A', 'B']);
    expect(ReactNoop.getChildren()).toEqual([span('A'), span('B')]);
  });
  it('suspends siblings and later recovers each independently', async () => {
    
    ReactNoop.render(
      <Fragment>
        <Suspense fallback={<Text text="Loading A..." />}>
          <AsyncText text="A" ms={5000} />
        </Suspense>
        <Suspense fallback={<Text text="Loading B..." />}>
          <AsyncText text="B" ms={6000} />
        </Suspense>
      </Fragment>,
    );
    expect(Scheduler).toFlushAndYield([
      'Suspend! [A]',
      'Loading A...',
      'Suspend! [B]',
      'Loading B...',
    ]);