Fix pipeline by adding testid "merge-request-assignee"

What does this MR do and why?

Fix pipeline https://jihulab.com/gitlab-cn/gitlab/-/pipelines/2917976/.

As Upstream: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/155729/diffs?pin=69121be4f1544a7f612e9855f5699029528cdfd0#69121be4f1544a7f612e9855f5699029528cdfd0_26_25

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