Add :sidekiq on migration spec

This should allow for workers to be cleared around the spec

Closes https://gitlab.com/gitlab-org/gitlab/issues/197482

spec/migrations/20190924152703_migrate_issue_trackers_data_spec.rb

@@ -3,7 +3,7 @@
 require 'spec_helper'
 require Rails.root.join('db', 'post_migrate', '20190924152703_migrate_issue_trackers_data.rb')
 
-describe MigrateIssueTrackersData, :migration do
+describe MigrateIssueTrackersData, :migration, :sidekiq do
   let(:services) { table(:services) }
   let(:migration_class) { Gitlab::BackgroundMigration::MigrateIssueTrackersSensitiveData }
   let(:migration_name)  { migration_class.to_s.demodulize }