fix: backend/package.json to reduce vulnerabilities

The following vulnerabilities are fixed with an upgrade:
- https://snyk.io/vuln/SNYK-JS-EXPRESS-6474509

backend/package.json

@@ -8,7 +8,7 @@
   "dependencies": {
     "cookie-parser": "~1.4.4",
     "debug": "~2.6.9",
-    "express": "~4.16.1",
+    "express": "~4.19.2",
     "morgan": "~1.9.1"
   }
 }