Bump next from 15.0.7 to 15.5.21

Bumps [next](https://github.com/vercel/next.js) from 15.0.7 to 15.5.21.
- [Release notes](https://github.com/vercel/next.js/releases)
- [Commits](vercel/next.js@v15.0.7...v15.5.21)

---
updated-dependencies:
- dependency-name: next
  dependency-version: 15.5.21
  dependency-type: direct:production
...

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Author: dependabot[bot]