Update selectors for QA::Page::Group::Show

What does this MR do?

Addresses https://gitlab.com/gitlab-org/gitlab-ce/issues/51893 and updates most of the selectors in https://gitlab.com/gitlab-org/gitlab-ee/blob/master/qa/qa/page/group/show.rb in line with the refactoring started in https://gitlab.com/gitlab-org/quality/team-tasks/issues/26

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/issues/51893

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Conforms to the code review guidelines
• Conforms to the merge request performance guidelines
• Conforms to the style guides
• Conforms to the database guides

Closes #51893 (closed)