Fix Style/OpenStructUse offenses

Changelog: other

.rubocop_manual_todo.yml

@@ -2580,7 +2580,6 @@ Style/OpenStructUse:
     - 'spec/graphql/mutations/clusters/agents/delete_spec.rb'
     - 'spec/graphql/mutations/commits/create_spec.rb'
     - 'spec/graphql/mutations/merge_requests/accept_spec.rb'
-    - 'spec/graphql/mutations/merge_requests/create_spec.rb'
     - 'spec/helpers/application_settings_helper_spec.rb'
     - 'spec/helpers/profiles_helper_spec.rb'
     - 'spec/initializers/doorkeeper_spec.rb'

spec/graphql/mutations/merge_requests/create_spec.rb

@@ -7,9 +7,10 @@ RSpec.describe Mutations::MergeRequests::Create do
 
   let_it_be(:project) { create(:project, :public, :repository) }
   let_it_be(:user) { create(:user) }
-  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: user },
       object: nil
     )