Change temp email suffix

What does this MR do and why?

Issue: https://jihulab.com/gitlab-cn/gitlab/-/issues/4577

临时邮箱不再使用 @gitlab.localhost 后缀，改用 commit_email_hostname。

commit_email_hostname 是指 UI 中做的配置，默认为 users.noreply.#{Gitlab.config.gitlab.host}：

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