Bump undici from 6.19.8 to 6.21.1

Bumps [undici](https://github.com/nodejs/undici) from 6.19.8 to 6.21.1.
- [Release notes](https://github.com/nodejs/undici/releases)
- [Commits](nodejs/undici@v6.19.8...v6.21.1)

---
updated-dependencies:
- dependency-name: undici
  dependency-type: direct:production
...

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Author: dependabot[bot]