Nested `startTransition` call "takes over" and makes parent `startTransition` unable to track `isPending`.

Seb says it's a bug.

Repro:

https://codesandbox.io/s/pensive-breeze-rg70wn?file=/IndexPage.js:192-288

1. Click the button
2. `isPending` in `IndexPage.js` is `true`

However, `isPending` in `App.js` is `false`.

Expected: `isPending` in `App.js` is also `true`.
if (!is(value, prevValue)) {
      
      const deferredLane = claimNextTransitionLane();
      currentlyRenderingFiber.lanes = mergeLanes(
        currentlyRenderingFiber.lanes,
        deferredLane,
      );
      markSkippedUpdateLanes(deferredLane);
      
      
      
      
      hook.baseState = true;
    }
     Reuse the previous value
    return prevValue;
  } else {
    
    
    
    
    
    
    
    
    if (hook.baseState) {
      
      hook.baseState = false;
      markWorkInProgressReceivedUpdate();
    }