chore(deps-dev): bump undici from 6.20.1 to 6.21.0

Bumps [undici](https://github.com/nodejs/undici) from 6.20.1 to 6.21.0.
- [Release notes](https://github.com/nodejs/undici/releases)
- [Commits](nodejs/undici@v6.20.1...v6.21.0)

---
updated-dependencies:
- dependency-name: undici
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

packages/multipart/package.json

@@ -100,7 +100,7 @@
     "ts-node": "^10.9.2",
     "tsc-alias": "^1.8.10",
     "typescript": "~5.6.3",
-    "undici": "^6.20.1"
+    "undici": "^6.21.0"
   },
   "dependencies": {
     "fastify-plugin": "^5.0.1"