Do not require `webpacker` in Active Job integration tests

Because `skip-javascript` option is specified for the dummy application
used in the integration tests.
bdc96802a7/activejob/test/support/integration/helper.rb (L14)

activejob/Rakefile

@@ -28,6 +28,7 @@ namespace :test do
 
   task "env:integration" do
     ENV["AJ_INTEGRATION_TESTS"] = "1"
+    ENV["SKIP_REQUIRE_WEBPACKER"] = "true"
   end
 
   ACTIVEJOB_ADAPTERS.each do |adapter|