Update screenshots to reflect the new group members view

What does this MR do?

Relates to &4233 (closed)

Over the last two milestones I have been working on an improved layout for the group members view. This is currently behind the vue_group_members_list feature flag but will be enabled this week on gitlab.com and then defaulted to on for %13.6. This MR updates the screenshots to reflect the new view.

GIF of new view for context

Related issues

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