chore(deps): bump express from 4.18.2 to 4.21.2 in /gurubu-backend

Bumps [express](https://github.com/expressjs/express) from 4.18.2 to 4.21.2.
- [Release notes](https://github.com/expressjs/express/releases)
- [Changelog](https://github.com/expressjs/express/blob/4.21.2/History.md)
- [Commits](expressjs/express@4.18.2...4.21.2)

---
updated-dependencies:
- dependency-name: express
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

gurubu-backend/package.json

@@ -13,7 +13,7 @@
     "body-parser": "^1.20.2",
     "cors": "^2.8.5",
     "dotenv": "^16.3.1",
-    "express": "^4.18.2",
+    "express": "^4.21.2",
     "openai": "^4.86.2",
     "redis": "^4.6.10",
     "socket.io": "^4.7.2",