Fix authorizations_controller_spec.rb for Doorkeeper v5.6.7

doorkeeper-gem/doorkeeper#1676 updated
the `render_error` to return a 400 Bad Request upon an error
instead of a 200. Adjust the spec accordingly.

spec/controllers/doorkeeper/authorizations_controller_spec.rb

@@ -82,14 +82,14 @@ def expect_successful_callback!
         it 'render error when client_id is missing' do
           authorize!(client_id: nil)
 
-          expect(response).to be_successful
+          expect(response).to have_http_status(:bad_request)
           expect(response).to render_template('doorkeeper/authorizations/error')
         end
 
         it 'render error when response_type is missing' do
           authorize!(response_type: nil)
 
-          expect(response).to be_successful
+          expect(response).to have_http_status(:bad_request)
           expect(response).to render_template('doorkeeper/authorizations/error')
         end
       end