Bump undici from 6.21.1 to 6.21.2 (Flagsmith#184)

Bumps [undici](https://github.com/nodejs/undici) from 6.21.1 to 6.21.2.
- [Release notes](https://github.com/nodejs/undici/releases)
- [Commits](nodejs/undici@v6.21.1...v6.21.2)

---
updated-dependencies:
- dependency-name: undici
  dependency-version: 6.21.2
  dependency-type: direct:development
...

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