build(deps-dev): bump undici from 6.21.1 to 6.21.3 in /docs/v3 (#4362)

Bumps [undici](https://github.com/nodejs/undici) from 6.21.1 to 6.21.3.
- [Release notes](https://github.com/nodejs/undici/releases)
- [Commits](nodejs/undici@v6.21.1...v6.21.3)

---
updated-dependencies:
- dependency-name: undici
  dependency-version: 6.21.3
  dependency-type: indirect
...

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

Author: dependabot[bot]