Bump next from 9.2.2 to 9.3.2 in /sandboxes/manual-tests/NextJS

Bumps [next](https://github.com/zeit/next.js) from 9.2.2 to 9.3.2.
- [Release notes](https://github.com/zeit/next.js/releases)
- [Commits](vercel/next.js@v9.2.2...v9.3.2)

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Author: dependabot[bot]