Ensure named path params are symbols (Fixes #16958)

actionpack/lib/action_dispatch/routing/route_set.rb

@@ -287,6 +287,7 @@ def handle_positional_args(controller_options, inner_options, args, result, path
               }
             end
 
+            inner_options.symbolize_keys!
             result.merge!(inner_options)
           end
         end

actionpack/test/dispatch/routing/route_set_test.rb

@@ -80,6 +80,14 @@ def call(env)
         assert_equal '/foo/1/bar/2', url_helpers.foo_bar_path(2, foo_id: 1)
       end
 
+      test "stringified controller and action keys are properly symbolized" do
+        draw do
+          root 'foo#bar'
+        end
+
+        assert_equal '/', url_helpers.root_path('controller' => 'foo', 'action' => 'bar')
+      end
+
       private
         def draw(&block)
           @set.draw(&block)