build(deps): bump undici from 6.21.0 to 6.21.1 in /docs (#6128)

Bumps [undici](https://github.com/nodejs/undici) from 6.21.0 to 6.21.1.
- [Release notes](https://github.com/nodejs/undici/releases)
- [Commits](nodejs/undici@v6.21.0...v6.21.1)

---
updated-dependencies:
- dependency-name: undici
  dependency-type: indirect
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]