Bump helmet from 7.2.0 to 8.1.0 in /backend

Bumps [helmet](https://github.com/helmetjs/helmet) from 7.2.0 to 8.1.0.
- [Changelog](https://github.com/helmetjs/helmet/blob/main/CHANGELOG.md)
- [Commits](https://github.com/helmetjs/helmet/compare/v7.2.0...v8.1.0)

---
updated-dependencies:
- dependency-name: helmet
  dependency-version: 8.1.0
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

backend/package-lock.json

@@ -16,7 +16,7 @@
         "dotenv": "^17.4.2",
         "express": "^4.18.2",
         "express-async-errors": "^3.1.1",
-        "helmet": "^7.1.0",
+        "helmet": "^8.1.0",
         "ioredis": "^5.3.2",
         "jsonwebtoken": "^9.0.2",
         "morgan": "^1.10.0",
@@ -4315,12 +4315,12 @@
       }
     },
     "node_modules/helmet": {
-      "version": "7.2.0",
-      "resolved": "https://registry.npmjs.org/helmet/-/helmet-7.2.0.tgz",
-      "integrity": "sha512-ZRiwvN089JfMXokizgqEPXsl2Guk094yExfoDXR0cBYWxtBbaSww/w+vT4WEJsBW2iTUi1GgZ6swmoug3Oy4Xw==",
+      "version": "8.1.0",
+      "resolved": "https://registry.npmjs.org/helmet/-/helmet-8.1.0.tgz",
+      "integrity": "sha512-jOiHyAZsmnr8LqoPGmCjYAaiuWwjAPLgY8ZX2XrmHawt99/u1y6RgrZMTeoPfpUbV96HOalYgz1qzkRbw54Pmg==",
       "license": "MIT",
       "engines": {
-        "node": ">=16.0.0"
+        "node": ">=18.0.0"
       }
     },
     "node_modules/html-escaper": {