fix: config type in RouteShorthandOptions

[BrianValente]

Hello! This PR fixes #5322.

Checklist

• run npm run test and npm run benchmark
• tests and/or benchmarks are included
• documentation is changed or added
• commit message and code follows the Developer's Certification of Origin
  and the Code of conduct

[mcollina]

Thanks for opening a PR! Can you please add a unit test? We use tsd for types.

[BrianValente]

@mcollina Sorry, but I couldn't find a way to test this. I'm not familiar with tsd, and the kind of test needed here is complex because it should encapsulate a type declaration just for the test.