Update to Node.js 20 compatibility

package.json

@@ -4,6 +4,9 @@
   "private": true,
   "description": "GitHub Action to run `npm audit`",
   "main": "lib/main.js",
+  "engines": {
+    "node": ">=20.0.0"
+  },
   "scripts": {
     "build": "tsc",
     "format": "prettier --write **/*.ts",
@@ -33,7 +36,7 @@
   },
   "devDependencies": {
     "@types/jest": "^29.5.5",
-    "@types/node": "^18.0.0",
+    "@types/node": "^20.0.0",
     "@typescript-eslint/parser": "^6.7.4",
     "@vercel/ncc": "^0.38.0",
     "eslint": "^8.51.0",