Bump mongoose from 7.5.3 to 8.8.3 in /backend

Bumps [mongoose](https://github.com/Automattic/mongoose) from 7.5.3 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@7.5.3...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

@@ -20,7 +20,7 @@
     "jsonwebtoken": "^9.0.2",
     "lodash": "^4.17.21",
     "mongodb-memory-server": "^8.15.1",
-    "mongoose": "^7.5.3",
+    "mongoose": "^8.8.3",
     "morgan": "^1.10.0",
     "nanoid": "^3.3.4",
     "pino": "^8.15.3",