Bump @types/express from 4.17.14 to 4.17.21 in /backend

Bumps [@types/express](https://github.com/DefinitelyTyped/DefinitelyTyped/tree/HEAD/types/express) from 4.17.14 to 4.17.21.
- [Release notes](https://github.com/DefinitelyTyped/DefinitelyTyped/releases)
- [Commits](https://github.com/DefinitelyTyped/DefinitelyTyped/commits/HEAD/types/express)

---
updated-dependencies:
- dependency-name: "@types/express"
  dependency-type: direct:development
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

backend/package-lock.json

@@ -24,7 +24,7 @@
     "@types/cors": "^2.8.12",
     "@types/eslint": "^8.44.3",
     "@types/eslint-plugin-prettier": "^3.1.0",
-    "@types/express": "^4.17.14",
+    "@types/express": "^4.17.21",
     "@types/geojson": "^7946.0.10",
     "@types/http-errors": "^2.0.1",
     "@types/jsonstream": "^0.8.31",