Change signUp signature to avoid tautology

[phoenix-ru]

          You're actually right, it's a weird implementation in https://github.com/sidebase/nuxt-auth/pull/615 which accepts two identical interfaces:

nuxt-auth/src/runtime/composables/local/useAuth.ts

Line 161 in 218a846

async function signUp(credentials: Credentials, signInOptions?: SecondarySignInOptions, signUpOptions?: SignUpOptions) {

It should be just signUpOptions, will probably move this to a different breaking change

Originally posted by @phoenix-ru in #702 (comment)