Add tests for no and bad phone number
Add tests for no and bad phone number

Adds two tests. One for the case of no phone number being supplied on
user creation (still creates a user with an empty string for phone
number), and the other for a phone number which fails the schema
validation (returns a 404).

AusDTO/dto-digitalmarketplace-buyer-frontend,alphagov/digitalmarketplace-buyer-frontend,alphagov/digitalmarketplace-buyer-frontend,AusDTO/dto-digitalmarketplace-buyer-frontend,alphagov/digitalmarketplace-buyer-frontend,AusDTO/dto-digitalmarketplace-buyer-frontend,alphagov/digitalmarketplace-buyer-frontend,AusDTO/dto-digitalmarketplace-buyer-frontend