Fix Style/OpenStructUse offenses in application settings helper

What does this MR do and why?

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

It replaces OpenStruct use since Ruby 3 discourages and replaces it by Struct.

Ideally, we want to use a "proper" object. See #358419.

File Change

• .rubocop_todo/style/open_struct_use.yml
• app/helpers/application_settings_helper.rb

MR acceptance checklist

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