fix: package.json & package-lock.json to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-COOKIE-8163060

Author: snyk-bot

package-lock.json

@@ -16,7 +16,7 @@
     "cors": "2.8.5",
     "cross-env": "7.0.3",
     "dotenv": "^16.4.5",
-    "express": "^4.19.2",
+    "express": "^4.21.1",
     "firebase": "^10.13.1",
     "firebase-admin": "^12.5.0",
     "gravatar": "^1.8.2",