Update reject-function-type.md

[TheJaredWilcurt]

Closes #1568

Improve example code to show @callback solution, and better differentiate variable names for clarity.

[brettz9]

Thanks for the PR! The docs though are generated from the .README templates and then supplied with—as is relevant for your changes—the tests in the test/rules/assertions folder. We'd need changes done in the tests file instead, and then run pnpm create-docs to update the generated files.

[TheJaredWilcurt]

I'll let you do that, pnpm only has experimental support by Volta, and I'd rather not mess with my environment for all my other repos to try to get this repo to work for a single PR. If it just used regular Node/npm then I'd give it a try, but I've gone years at this point without seeing a Yarn or pnpm repo, so I don't think it's worth it to mess with that for me.

[brettz9]

I'll let you do that, pnpm only has experimental support by Volta, and I'd rather not mess with my environment for all my other repos to try to get this repo to work for a single PR. If it just used regular Node/npm then I'd give it a try, but I've gone years at this point without seeing a Yarn or pnpm repo, so I don't think it's worth it to mess with that for me.

Sure, done. If you value disk space and create a lot of repos, you're missing out on pnpm though. I couldn't fit all the repos I have on my machine if I weren't using pnpm for most of them. Hopefully Volta support will be upgraded.