Fix impersonate button background color
Small regression was introduced when the background was removed in https://gitlab.com/gitlab-org/gitlab/-/merge_requests/213854+s. ![image](/uploads/120626a5d0117f7a717cc1216f72d316/image.png){width=245 height=124} ![image](/uploads/cb16ae35f92f8e4df8aff29ba52aa858/image.png){width=245 height=124}
issue