Prefer usage of helper `expanded_by_default?`

What does this MR do?

This MR replaces all usages of Rails.env.test? with the corresponding helper method expanded_by_default?

CE Backport: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/27729

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content