please fix z.coerce.boolean() for "false" #3924

Note — Boolean coercion with z.coerce.boolean() may not work how you expect. Any truthy value is coerced to true, and any falsy value is coerced to false.

This is not intuitive and irrational. Please fix z.coerce.boolean() to produce false from "false".

Otherwise we can safely assume that coerce is simply broken (!) for booleans.