Fix OpenStruct use

Fixed OpenStruct use as Ruby 3 discourages it

Changelog: other
EE: true

.rubocop_manual_todo.yml

@@ -2556,7 +2556,6 @@ Style/OpenStructUse:
     - 'ee/spec/features/projects/new_project_spec.rb'
     - 'ee/spec/finders/template_finder_spec.rb'
     - 'ee/spec/graphql/ee/resolvers/board_lists_resolver_spec.rb'
-    - 'ee/spec/graphql/resolvers/board_groupings/epics_resolvers_spec.rb'
     - 'ee/spec/helpers/ee/blob_helper_spec.rb'
     - 'ee/spec/lib/gitlab/auth/group_saml/failure_handler_spec.rb'
     - 'ee/spec/lib/gitlab/legacy_github_import/project_creator_spec.rb'

ee/spec/graphql/resolvers/board_groupings/epics_resolvers_spec.rb

@@ -29,9 +29,9 @@ RSpec.describe Resolvers::BoardGroupings::EpicsResolver do
   let_it_be(:epic_issue2) { create(:epic_issue, epic: epic2, issue: issue2) }
   let_it_be(:epic_issue3) { create(:epic_issue, epic: epic3, issue: issue3) }
 
-  let_it_be(:context) do
+  let(:context) do
     GraphQL::Query::Context.new(
-      query: OpenStruct.new(schema: nil),
+      query: double('query', schema: nil),
       values: { current_user: current_user },
       object: nil
     )