Fix ActiveSupport::TestCase being loaded too early

rails/rails@76966f9 implemented configuration to report assertionless tests. But the configuration causes ActiveSupport::TestCase to be loaded too early in the boot process. It causes issues when other engines define load hooks on :active_support_test_case because they are run immediately. Instead, we should wrap the configuration in a load hook so it gets set at the appropriate time.

Author: andrewn617

activesupport/lib/active_support/railtie.rb

@@ -125,7 +125,9 @@ class Railtie < Rails::Railtie # :nodoc:
         elsif k == :use_rfc4122_namespaced_uuids
           ActiveSupport.deprecator.warn("config.active_support.use_rfc4122_namespaced_uuids is deprecated and will be removed in Rails 7.2.")
         elsif k == :assertionless_tests_behavior
-          ActiveSupport::TestCase.assertionless_tests_behavior = v
+          ActiveSupport.on_load(:active_support_test_case) do
+            ActiveSupport::TestCase.assertionless_tests_behavior = v
+          end
         else
           k = "#{k}="
           ActiveSupport.public_send(k, v) if ActiveSupport.respond_to? k