actionpack: fix url_helpers to return includable module type (#977)

* actionpack: add test for url_helpers include

* actionpack: fix url_helpers to return includable module type

Author: aruma256

gems/actionpack/7.2/_test/test.rb

@@ -7,3 +7,7 @@ class BarController < ActionController::Base
 end
 
 ActionController::Base.new.render_to_string(template: 'foo', locals: { bar: 'baz' })
+
+class FooService
+  include ActionDispatch::Routing::RouteSet.new.url_helpers
+end

gems/actionpack/7.2/_test/test.rbs

@@ -3,3 +3,6 @@ end
 
 class BarController < ActionController::Base
 end
+
+class FooService
+end

gems/actionpack/7.2/actiondispatch.rbs

@@ -71,7 +71,7 @@ module ActionDispatch
     class RouteSet
       def draw: () { () [self: Mapper] -> untyped } -> nil
 
-      def url_helpers: (?bool supports_path) -> RouteSet_AnonymousModule
+      def url_helpers: (?bool supports_path) -> singleton(RouteSet_AnonymousModule)
 
       module RouteSet_AnonymousModule
         include ActiveSupport::Concern