docs: upgrade Node.js to version 20

Node.js 20 is the current LTS release:
https://nodejs.org/en/about/releases/

BREAKING CHANGE: the minimum Node.js is 20

Author: coderbyheart

.github/workflows/test-and-release.yaml

@@ -13,7 +13,7 @@ jobs:
       - uses: actions/checkout@v4
       - uses: actions/setup-node@v4
         with:
-          node-version: "18.x"
+          node-version: "20.x"
       - name: Keep npm cache around to speed up installs
         uses: actions/cache@v3
         with:

package.json

@@ -63,7 +63,7 @@
     ]
   },
   "engines": {
-    "node": ">=18",
+    "node": ">=20",
     "npm": ">=9"
   },
   "release": {