Fix Pipeline 2378706

What does this MR do and why?

Fix Pipeline https://jihulab.com/gitlab-cn/gitlab/-/pipelines/2378706

1. 在 Spec 中创建 User 时，需要加上 :with_namespace 参数

Related Upstream MR：https://gitlab.com/gitlab-org/gitlab/-/merge_requests/137713

Failed Job: https://jihulab.com/gitlab-cn/gitlab/-/jobs/12228781

Upstream 修改了 Spec 部分的代码，使用 create(:user) 时不再自动创建 Namespace，需要加上 :with_namespace。

2. 解决 Grape::Validations::Base 带来的 Warning 信息

Failed Job: https://jihulab.com/gitlab-cn/gitlab/-/jobs/12231772

- Grape::Validations::Base
+ Grape::Validations::Validators::Base

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