Fix sidekiq test order dependency

Requiring sidekiq/testing changes stuff, so we need to counteract that
after we do so.

And given its potential to confuse things, let's do it up front, at a
predictable point.

activejob/test/integration/queuing_test.rb

@@ -26,8 +26,6 @@ class QueuingTest < ActiveSupport::TestCase
 
   test 'should supply a wrapped class name to Sidekiq' do
     skip unless adapter_is?(:sidekiq)
-    require 'sidekiq/testing'
-
     Sidekiq::Testing.fake! do
       ::HelloJob.perform_later
       hash = ActiveJob::QueueAdapters::SidekiqAdapter::JobWrapper.jobs.first

activejob/test/support/integration/adapters/sidekiq.rb

 require 'sidekiq/api'
 
+require 'sidekiq/testing'
+Sidekiq::Testing.disable!
+
 module SidekiqJobsManager
 
   def setup