ensure that nullable is not set for required parameters

[erikbrinkman]

nullable was enforced for optional parameters, but not forbidden for required parameters. This tests and enforces the latter case.

What issue does this pull request resolve?

fixes #2030

at least partially

What changes did you make?

add nullable?: false and tests

Is there anything that requires more attention while reviewing?

nope

[erikbrinkman]

I should note that typescript 4.8 causes errors with the JTD schema type, so I restricted the typescript version too.

[epoberezkin]

Fixed the error in 4.8 now, so made it >= 4.8