## Summary
Since we are enabling `useModernStrictMode` flag internally, to make
sure the internal testing of half StrictMode doesn't suddenly break,
this PR makes sure it also works with `useModernStrictMode` true.
## Test plan:
Manually set `useModernStrictMode` to true.
`yarn test ReactOffscreenStrictMode-test -r=www-modern --env=development
--variant=true`
`yarn test ReactStrictMode-test.internal -r=www-modern --env=development
--variant=true`
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