Update `group_saml_group_managed_accounts_spec` spec to account for SAML user provisioning

We implemented SAML user provisioning in %13.7 but the related group_saml_group_managed_accounts_spec end-to-end still expects the user registration screen to be shown when a new user with a unique email address tries to log into a GMA enabled group. This test has been in quarantine due to a bug that has now been closed because of the new flow.

This issue is to update the end-to-end test to account for automatic SAML user provisioning.