Fix sign up not returning group with unique path/name

What does this MR do and why?

Fixes SaaS signup group project unique URL does not a... (#375629 - closed)

Screenshots or screen recordings

Before	After
form returns with same group name	form returns with unique group name and resulting path

How to set up and validate locally

1. Visit http://localhost:3000/users/sign_up/groups_projects
2. Enter a group name that is already present, and very quickly click create project before the javascript in the background changes the path to a unique one.

MR acceptance checklist

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