Node 16 is deprecated

[bhubavenski]

Hello, Steve. I wanted to let you know that Node.js 16 is deprecated and GitHub Actions no longer support it. It might be a good idea to update your notes at https://stevekinney.net/courses/testing/continuous-integration. Additionally, you could include a note for users of different package managers like me (I use pnpm), so they are aware that their package manager requires a different setup.