Update dependency helmet to v8

Author: renovate[bot]

backend/package.json

@@ -16,7 +16,7 @@
     "connect-redis": "^7.1.0",
     "redis": "^4.6.12",
     "openid-client": "^5.6.4",
-    "helmet": "^7.1.0",
+    "helmet": "^8.0.0",
     "cors": "^2.8.5",
     "compression": "^1.7.4",
     "express-rate-limit": "^8.0.0",