Bump undici from 5.24.0 to 5.26.3 in /backend (#65)

Bumps [undici](https://github.com/nodejs/undici) from 5.24.0 to 5.26.3.
- [Release notes](https://github.com/nodejs/undici/releases)
- [Commits](nodejs/undici@v5.24.0...v5.26.3)

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

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