CI: Fix cookbook test script

When I removed the cookbook-loader.mjs, I accidentally broke the
test-cookbook-one script in package.json. It made the tests always pass
because the actual test was no longer loaded due to the presence of the
--eval command line argument. Instead, use --require to define a global
assert property.

Author: ptomato

docs/cookbook/assert.js

@@ -0,0 +1 @@
+globalThis.assert = require('node:assert').strict;

polyfill/package.json

@@ -9,7 +9,7 @@
   "scripts": {
     "test": "node ./test/all.mjs",
     "test-cookbook": "npm run build && TEST=all npm run test-cookbook-one",
-    "test-cookbook-one": "node --require=./script.js --eval='globalThis.assert = require(`node:assert`).strict' ../docs/cookbook/$TEST.mjs",
+    "test-cookbook-one": "node --require=./script.js --require=../docs/cookbook/assert.js ../docs/cookbook/$TEST.mjs",
     "test262": "npm run build262 && node runtest262.mjs",
     "codecov:test262": "./ci_codecov_test262.sh",
     "build": "rollup -c rollup.config.js --bundleConfigAsCjs",