Bump undici from 6.26.0 to 6.28.0 in /bot

Bumps [undici](https://github.com/nodejs/undici) from 6.26.0 to 6.28.0.
- [Release notes](https://github.com/nodejs/undici/releases)
- [Commits](nodejs/undici@v6.26.0...v6.28.0)

---
updated-dependencies:
- dependency-name: undici
  dependency-version: 6.28.0
  dependency-type: indirect
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]