[refactor](auth): Simplify workspace lookup and cleanup UI logic

Streamlined workspace selection by defaulting to the first available workspace. Adjusted conditional rendering for a separator between authentication providers, improving clarity and reducing redundancy. Minor formatting changes were also applied for consistency.

packages/twenty-front/src/modules/auth/sign-in-up/components/SignInUpGlobalScopeForm.tsx

@@ -107,9 +107,9 @@ export const SignInUpGlobalScopeForm = () => {
     <>
       <StyledContentContainer>
         {authProviders.google && <SignInUpWithGoogle />}
-
         {authProviders.microsoft && <SignInUpWithMicrosoft />}
-        <HorizontalSeparator visible />
+        {authProviders.google ||
+          (authProviders.microsoft && <HorizontalSeparator visible />)}
         {/* eslint-disable-next-line react/jsx-props-no-spreading */}
         <FormProvider {...form}>
           <StyledForm onSubmit={form.handleSubmit(handleSubmit)}>