Fix email bug when signup with errors

What does this MR do and why?

Upstream related MR: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/105983/diffs

Failed pipeline in JH: https://jihulab.com/gitlab-cn/gitlab/-/jobs/5800202

Upstream changed the _signup_box.html.haml, JH put a new haml file to override it: jh/app/views/devise/shared/_signup_box.html.haml.