build(deps-dev): bump qs from 6.14.2 to 6.15.2 in /backend

Bumps [qs](https://github.com/ljharb/qs) from 6.14.2 to 6.15.2.
- [Changelog](https://github.com/ljharb/qs/blob/main/CHANGELOG.md)
- [Commits](https://github.com/ljharb/qs/compare/v6.14.2...v6.15.2)

---
updated-dependencies:
- dependency-name: qs
  dependency-version: 6.15.2
  dependency-type: indirect
...

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

backend/package-lock.json

@@ -4473,9 +4473,9 @@
       }
     },
     "node_modules/qs": {
-      "version": "6.14.2",
-      "resolved": "https://registry.npmjs.org/qs/-/qs-6.14.2.tgz",
-      "integrity": "sha512-V/yCWTTF7VJ9hIh18Ugr2zhJMP01MY7c5kh4J870L7imm6/DIzBsNLTXzMwUA3yZ5b/KBqLx8Kp3uRvd7xSe3Q==",
+      "version": "6.15.2",
+      "resolved": "https://registry.npmjs.org/qs/-/qs-6.15.2.tgz",
+      "integrity": "sha512-Rzq0KEyX/w/tEybncDgdkZrJgVUsUMk3xjh3t5bv3S1HTAtg+uOYt72+ZfwiQwKdysThkTBdL/rTi6HDmX9Ddw==",
       "dev": true,
       "license": "BSD-3-Clause",
       "dependencies": {