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`.
const [showA, _setShowA] = useState(false);
        const [showB, _setShowB] = useState(false);
        const [showC, _setShowC] = useState(false);
        setShowA = _setShowA;
        setShowB = _setShowB;
        setShowC = _setShowC;
        
        
        
        
        
        
        
        return (
          <>
            <Suspense fallback={<Text text="Loading..." />}>
              {showA ? <AsyncText text="A" /> : null}
              {showB ? <AsyncText text="B" /> : null}
              {showC ? <AsyncText text="C" /> : null}
            </Suspense>
          </>
        );