Bump mongoose from 6.13.0 to 8.8.3 in /backend

Bumps [mongoose](https://github.com/Automattic/mongoose) from 6.13.0 to 8.8.3.
- [Release notes](https://github.com/Automattic/mongoose/releases)
- [Changelog](https://github.com/Automattic/mongoose/blob/master/CHANGELOG.md)
- [Commits](Automattic/mongoose@6.13.0...8.8.3)

---
updated-dependencies:
- dependency-name: mongoose
  dependency-type: direct:production
...

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

Author: dependabot[bot]

backend/package-lock.json

@@ -10,7 +10,7 @@
     "cors": "^2.8.5",
     "express": "^4.21.0",
     "fast-xml-parser": "^4.3.2",
-    "mongoose": "^6.13.0",
+    "mongoose": "^8.8.3",
     "var": "^0.4.0",
     "web-vitals": "^2.1.4",
     "xml2js": "^0.6.0"