Migrate deprecated 'assert' import syntax, bump to Node 18.20 (#35826)

* Remove deprecated 'assert' import syntax in favor of 'with'

fixes #35825

* Set minimum Node version in `.engines` field to 18.20.0

This is the minimum version that supports the new `import ... with`
syntax.

package.json

@@ -14,7 +14,7 @@
     "url": "git+https://github.com/mdn/content.git"
   },
   "engines": {
-    "node": ">=18.18.0"
+    "node": ">=18.20.0"
   },
   "type": "module",
   "scripts": {

scripts/up-to-date-check.js

@@ -1,5 +1,5 @@
-import yariPackageJson from "@mdn/yari/package.json" assert { type: "json" };
-import thisPackageJson from "../package.json" assert { type: "json" };
+import yariPackageJson from "@mdn/yari/package.json" with { type: "json" };
+import thisPackageJson from "../package.json" with { type: "json" };
 
 const availableYariVersion = thisPackageJson.dependencies["@mdn/yari"];
 const installedYariVersion = yariPackageJson.version;