Fix a minor UI bug introduced in https://codeberg.org/forgejo/forgejo/pulls/6112.
The condition `if .EnableInternalSignIn` was added to display of the divider, but it is only available when `oauth_container.tmpl` is called from signIn page, it is not relevant to signUp page.
Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/6463
Reviewed-by: Earl Warren <earl-warren@noreply.codeberg.org>
Setting ENABLE_INTERNAL_SIGNIN to false will disable the built-in
signin form, should the administrator prefer to limit users to SSO.
Continuation of forgejo/forgejo#6076
