Test that `dodola.services.validate` actually fails bad data

We test `dodola.services.validate` in `dodola.tests.test_services.test_validation()` for the "happy path" (well-behaved data), but it would be great if we could test to ensure validation correctly catches each of the conditions that it's supposed to catch.

I think I've mentioned this in a few previous PRs, but I'm putting it here so we dont' forget.