Add test case for arel_attribute with a custom table

Since #29301, `arel_attribute` respects a custom table name.

activerecord/test/cases/relations_test.rb

@@ -1806,6 +1806,10 @@ def test_presence
     assert_equal post, custom_post_relation.joins(:author).where!(title: post.title).take
   end
 
+  test "arel_attribute respects a custom table" do
+    assert_equal [posts(:welcome)], custom_post_relation.ranked_by_comments.limit_by(1).to_a
+  end
+
   test "#load" do
     relation = Post.all
     assert_queries(1) do

activerecord/test/models/post.rb

@@ -21,7 +21,7 @@ def greeting
 
   scope :containing_the_letter_a, -> { where("body LIKE '%a%'") }
   scope :titled_with_an_apostrophe, -> { where("title LIKE '%''%'") }
-  scope :ranked_by_comments,      -> { order("comments_count DESC") }
+  scope :ranked_by_comments, -> { order(arel_attribute(:comments_count).desc) }
 
   scope :limit_by, lambda { |l| limit(l) }
   scope :locked, -> { lock }