Bump undici from 5.26.4 to 5.28.4 in /.github/fill-template

Bumps [undici](https://github.com/nodejs/undici) from 5.26.4 to 5.28.4.
- [Release notes](https://github.com/nodejs/undici/releases)
- [Commits](nodejs/undici@v5.26.4...v5.28.4)

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

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