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.
expect(ReactNoop.getChildren()).toEqual([span('A')]);
    ReactNoop.render(<Foo showB={true} />);
    expect(Scheduler).toFlushAndYield([
      'Foo',
      'A',
      'Suspend! [B]',
      'Loading B...',
    ]);
    
    expect(ReactNoop.getChildren()).toEqual([span('A')]);
    
    Scheduler.unstable_advanceTime(600);
    await advanceTimers(600);
    expect(ReactNoop.getChildren()).toEqual([span('A'), span('Loading B...')]);
  });
  it('commits a suspended idle pri render within a reasonable time', async () => {
    function Foo({renderContent}) {
      return (
        <Fragment>
          <Suspense fallback={<Text text="Loading A..." />}>
            {renderContent ? <AsyncText text="A" ms={10000} /> : null}
          </Suspense>
        </Fragment>
      );
    }
    ReactNoop.render(<Foo />);
    expect(Scheduler).toFlushAndYield([]);
    ReactNoop.render(<Foo renderContent={1} />);