Bump undici from 5.28.1 to 5.28.4 in /backend

Bumps [undici](https://github.com/nodejs/undici) from 5.28.1 to 5.28.4.
- [Release notes](https://github.com/nodejs/undici/releases)
- [Commits](https://github.com/nodejs/undici/compare/v5.28.1...v5.28.4)

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

Signed-off-by: dependabot[bot] <support@github.com>

backend/package-lock.json

@@ -4888,9 +4888,9 @@
       }
     },
     "node_modules/undici": {
-      "version": "5.28.1",
+      "version": "5.28.4",
-      "resolved": "https://registry.npmjs.org/undici/-/undici-5.28.1.tgz",
+      "resolved": "https://registry.npmjs.org/undici/-/undici-5.28.4.tgz",
-      "integrity": "sha512-xcIIvj1LOQH9zAL54iWFkuDEaIVEjLrru7qRpa3GrEEHk6OBhb/LycuUY2m7VCcTuDeLziXCxobQVyKExyGeIA==",
+      "integrity": "sha512-72RFADWFqKmUb2hmmvNODKL3p9hcB6Gt2DOQMis1SEBaV6a4MH8soBvzg+95CYhCKPFedut2JY9bMfrDl9D23g==",
       "dependencies": {
         "@fastify/busboy": "^2.0.0"
       },