Disable Rails/SaveBang cop for subscriptions_controller_spec.rb

As it results in active record validation failure.

ee/spec/controllers/subscriptions_controller_spec.rb

@@ -237,7 +237,7 @@ RSpec.describe SubscriptionsController do
         let(:group) { Group.new(path: 'foo') }
 
         it 'returns the errors in json format' do
-          group.save!
+          group.save # rubocop:disable Rails/SaveBang
           subject
 
           expect(response.body).to include({ name: ["can't be blank"] }.to_json)
@@ -247,7 +247,7 @@ RSpec.describe SubscriptionsController do
           let(:group) { Group.new(path: 'foo', name: '<script>alert("attack")</script>') }
 
           it 'returns the errors in json format' do
-            group.save!
+            group.save # rubocop:disable Rails/SaveBang
             subject
 
             expect(Gitlab::Json.parse(response.body)['name']).to match_array([Gitlab::Regex.group_name_regex_message, HtmlSafetyValidator.error_message])