Fix Style/OpenStructUse offenses for import service and spec helpers

What does this MR do and why?

This MR aims to solve the issue #344279 (closed)

Fixes OpenStruct use since Ruby 3 discourages it.

File Change

• .rubocop_todo/style/open_struct_use.yml
• spec/services/projects/import_service_spec.rb
• spec/support/helpers/import_spec_helper.rb
• spec/support/helpers/login_helpers.rb

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.