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

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-BODYPARSER-7926860
- https://snyk.io/vuln/SNYK-JS-EXPRESS-7926867
- https://snyk.io/vuln/SNYK-JS-SEND-7926862
- https://snyk.io/vuln/SNYK-JS-SERVESTATIC-7926865

package.json

@@ -23,7 +23,7 @@
     "cookie-parser": "^1.4.6",
     "cors": "^2.8.5",
     "dotenv-flow": "^4.1.0",
-    "express": "^4.19.2",
+    "express": "^4.21.0",
     "express-session": "^1.18.0",
     "express-validator": "^7.2.0",
     "helmet": "^7.1.0",