Provide a not tester

[edgarmueller]

Describe the bug
A negation tester would be useful in certain scenarios, e.g. when checking that a schema is not of type object, for instance not(schemaTypeIs('object'))

To Reproduce
Right now there's no easy way to do that, rather one'd have to check via or(schemaTypeIs('number'), schemaTypeIs('integer'), ...) and so on.

Expected behavior
A not tester that negates the result.