E2E: Add search_member to parent_group_access_termination_spec

What does this MR do and why?

This MR adds the search_member method to parent_group_access_termination_spec in order to filter the group members page for that specific member before attempting to remove them. This will help the test be more robust and prevent failures such as #386895 (closed), where the group had multiple pages of members due to an unrelated issue with our test deletion script at the time.

MR acceptance checklist

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