Bump undici from 6.20.1 to 6.21.0

Bumps [undici](https://github.com/nodejs/undici) from 6.20.1 to 6.21.0.
- [Release notes](https://github.com/nodejs/undici/releases)
- [Commits](nodejs/undici@v6.20.1...v6.21.0)

---
updated-dependencies:
- dependency-name: undici
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>