REFACTOR: fix code review comments2

- rspec rewording
- argument type

lib/api/todos.rb

@@ -43,7 +43,7 @@ module API
           optional :action, String, values: Todo::ACTION_NAMES.values.map(&:to_s)
           optional :author_id, Integer
           optional :state, String, values: Todo.state_machine.states.map(&:name).map(&:to_s)
-          optional :type, Array[String], values: TodosFinder.todo_types
+          optional :type, String, values: TodosFinder.todo_types
           optional :project_id, Integer
           optional :group_id, Integer
         end

spec/requests/api/todos_spec.rb

@@ -43,14 +43,14 @@ RSpec.describe API::Todos do
         end
 
         context "invalid state" do
-          it 'returns argument error' do
+          it 'returns 400' do
             get api('/todos', john_doe), params: { state: 'InvalidState' }
             expect(response).to have_gitlab_http_status(:bad_request)
           end
         end
 
         context "invalid type" do
-          it 'returns argument error' do
+          it 'returns 400' do
             get api('/todos', john_doe), params: { type: 'InvalidType' }
             expect(response).to have_gitlab_http_status(:bad_request)
           end