fix: package.json & yarn.lock 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

@@ -73,7 +73,7 @@
     "eslint-plugin-json": "^2.1.1",
     "eslint-plugin-prettier": "^3.1.4",
     "eslint-plugin-react": "7.26.1",
-    "express": "^4.17.3",
+    "express": "^4.21.0",
     "fake-indexeddb": "^2.0.4",
     "front-matter": "^2.3.0",
     "fs-extra": "^9.0.1",