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`.
let act;
let getCacheForType;
let waitForAll;
let waitFor;
let waitForPaint;
let assertLog;
let caches;
let seededCache;
describe('ReactTransition', () => {
  beforeEach(() => {
    jest.resetModules();
    React = require('react');
    ReactNoop = require('react-noop-renderer');
    Scheduler = require('scheduler');
    useState = React.useState;
    useLayoutEffect = React.useLayoutEffect;
    useTransition = React.useTransition;
    Suspense = React.Suspense;
    startTransition = React.startTransition;
    getCacheForType = React.unstable_getCacheForType;
    act = require('internal-test-utils').act;
    const InternalTestUtils = require('internal-test-utils');
    waitForAll = InternalTestUtils.waitForAll;
    waitFor = InternalTestUtils.waitFor;
    waitForPaint = InternalTestUtils.waitForPaint;
    assertLog = InternalTestUtils.assertLog;
    caches = [];
    seededCache = null;
  });
  function createTextCache() {