Only automatically include validations when they are enabled on `has_secure_password`

This is a follow up to #16024.
This test was testing the behaviour of `has_secure_password(validations: false)`, so it is using the `Visitor` model. It was testing that when that flag is false it won't be adding the validation rules. However I think the new test right above this one is probably enough, and I am leaning towards just :scissors: this test. WDYT?