Add missing return statement in if_not_unset validator

[bysiber]

Summary

if_not_unset() defines an inner validate function but never returns it, so all attrs fields using this validator have no validation at all.

Problem

def if_not_unset(validator: Callable[[Any, Any, Any], None]) -> None:
    def validate(instance: Any, attribute: Any, value: Any) -> None:
        if value is unset:
            return
        validator(instance, attribute, value)
    # missing: return validate

The function implicitly returns None, so attrs treats the field as having no validator. This affects TaskDefaults.job_executor and all TaskParameters fields — they accept any value without validation.

Fix

Add return validate at the end of the function.

[agronholm]

Good catch, thanks!

[coveralls]

coverage: 92.63%. first build
when pulling eebe2f4 on bysiber:fix/if-not-unset-missing-return
into f2337f7 on agronholm:master.