added api-courses spec and test

[linear[bot]]

DX-834

[vercel[bot]]

This pull request is being automatically deployed with Vercel (learn more).
To see the status of your deployment, click below or on the icon next to each commit.

🔍 Inspect: https://vercel.com/cypress-io/cypress-realworld-testing-course-app/8MGeaXquphAtz1JPrQQz6SCegimu
✅ Preview: https://cypress-realworld-testing-course-app-git-dx-8-e20a6b-cypress-io.vercel.app

[robertguss]

@kevinold this is a new spec and test for the next.js content for learning how to test API response payloads.