Don't use JSONObject for `transform`.

[A5rocks]

Checklist

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

I'll use CI to make sure npm run test and npm run benchmark are AOK. I can elaborate on why this change is necessary, but instead just look at the changes to the tests. BTW the example in the readme still works (once you change it by making transformedSchema be ...ts then const transformedSchema = ts as FastifySchema).

[A5rocks]

Hi! Maybe the Windows flakiness is gone now?

[mcollina]

This can land! thx

[A5rocks]

Thank you!