Bump next from 9.5.3 to 9.5.4 in /test/docker/app

Bumps [next](https://github.com/vercel/next.js) from 9.5.3 to 9.5.4.
- [Release notes](https://github.com/vercel/next.js/releases)
- [Changelog](https://github.com/vercel/next.js/blob/canary/release.js)
- [Commits](vercel/next.js@v9.5.3...v9.5.4)

Signed-off-by: dependabot[bot] <support@github.com>