Make sure that ActionController::Api can include helpers

Closes #28554

actionpack/test/controller/api/with_helpers_test.rb

@@ -0,0 +1,26 @@
+require "abstract_unit"
+
+module ApiWithHelper
+  def my_helper
+    "helper"
+  end
+end
+
+class WithHelpersController < ActionController::API
+  include ActionController::Helpers
+  helper ApiWithHelper
+
+  def with_helpers
+    render plain: self.class.helpers.my_helper
+  end
+end
+
+class WithHelpersTest < ActionController::TestCase
+  tests WithHelpersController
+
+  def test_with_helpers
+    get :with_helpers
+
+    assert_equal "helper", response.body
+  end
+end