Fix regression introduced in 8cf0f51eb2.

spec/serializers/admin_plugin_serializer_spec.rb

@@ -0,0 +1,14 @@
+require 'rails_helper'
+
+RSpec.describe AdminPluginSerializer do
+  let(:instance) { Plugin::Instance.new }
+
+  subject { described_class.new(instance) }
+
+  describe 'enabled_setting' do
+    it 'should return the right value' do
+      instance.enabled_site_setting('test')
+      expect(subject.enabled_setting).to eq('test')
+    end
+  end
+end