chore(deps): bump undici from 6.20.1 to 6.21.1 in /test/load (#4227)

Bumps [undici](https://github.com/nodejs/undici) from 6.20.1 to 6.21.1.
- [Release notes](https://github.com/nodejs/undici/releases)
- [Commits](https://github.com/nodejs/undici/compare/v6.20.1...v6.21.1)

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

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

test/load/package-lock.json

@@ -11072,9 +11072,10 @@
       }
     },
     "node_modules/undici": {
-      "version": "6.20.1",
-      "resolved": "https://registry.npmjs.org/undici/-/undici-6.20.1.tgz",
-      "integrity": "sha512-AjQF1QsmqfJys+LXfGTNum+qw4S88CojRInG/6t31W/1fk6G59s92bnAvGz5Cmur+kQv2SURXEvvudLmbrE8QA==",
+      "version": "6.21.1",
+      "resolved": "https://registry.npmjs.org/undici/-/undici-6.21.1.tgz",
+      "integrity": "sha512-q/1rj5D0/zayJB2FraXdaWxbhWiNKDvu8naDT2dl1yTlvJp4BLtOcp2a5BvgGNQpYYJzau7tf1WgKv3b+7mqpQ==",
+      "license": "MIT",
       "engines": {
         "node": ">=18.17"
       }