fix: package.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

@@ -42,7 +42,7 @@
     "csurf": "^1.11.0",
     "directory-tree": "^2.2.5",
     "dotenv": "^8.2.0",
-    "express": "^4.17.1",
+    "express": "^4.21.0",
     "express-rate-limit": "^5.1.3",
     "flat": "^5.0.0",
     "github-slugger": "^1.2.1",