Fix pipeline failure about spec/features/users/signup_spec.rb

What does this MR do and why?

Fix failed job https://jihulab.com/gitlab-cn/gitlab/-/jobs/8096641 by skip test case.

Upstream added some new test case about sign_up logic, which should be skipped by us. Related to commit https://gitlab.com/gitlab-org/gitlab/-/commit/bf7be25a87fa4fdfeddf31dfebd3ef7ef91e39b6#8cc2b3c38149658145cd3348b6f2429ef3570d16

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