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`.
useId(): string {
      currentHookNameInDev = 'useId';
      mountHookTypesDev();
      return mountId();
    },
  };
  if (enableCache) {
    (HooksDispatcherOnMountInDEV: Dispatcher).useCacheRefresh =
      function useCacheRefresh() {
        currentHookNameInDev = 'useCacheRefresh';
        mountHookTypesDev();
        return mountRefresh();
      };
  }
  if (enableUseHook) {
    (HooksDispatcherOnMountInDEV: Dispatcher).use = use;
  }
  if (enableUseMemoCacheHook) {
    (HooksDispatcherOnMountInDEV: Dispatcher).useMemoCache = useMemoCache;
  }
  if (enableUseEffectEventHook) {
    (HooksDispatcherOnMountInDEV: Dispatcher).useEffectEvent =
      function useEffectEvent<Args, Return, F: (...Array<Args>) => Return>(
        callback: F,
      ): F {
        currentHookNameInDev = 'useEffectEvent';
        mountHookTypesDev();
        return mountEvent(callback);
      };
  }