Fix eager_loading? when ordering with Hash syntax

`eager_loading?` is triggered correctly when using `order` with
hash syntax on an outer table.

before:
```ruby
Post.includes(:comments).order({ "comments.label": :ASC }).eager_loading?
=> raises ActiveRecord::StatementInvalid
```

after:
```ruby
Post.includes(:comments).order({ "comments.label": :ASC }).eager_loading?
=> true
```

Co-authored-by: Eugene Kenny <elkenny@gmail.com>

activerecord/CHANGELOG.md

@@ -1,3 +1,15 @@
+*   Fix `eager_loading?` when ordering with `Hash` syntax
+
+    `eager_loading?` is triggered correctly when using `order` with hash syntax
+    on an outer table.
+
+    ```ruby
+    Post.includes(:comments).order({ "comments.label": :ASC }).eager_loading?
+    => true
+    ```
+
+    *Jacopo Beschi*
+
 *   Move the forcing of clear text encoding to the `ActiveRecord::Encryption::Encryptor`.
 
     Fixes #42699.

activerecord/lib/active_record/relation/query_methods.rb

@@ -1548,7 +1548,14 @@ module ActiveRecord
       end
 
       def column_references(order_args)
-        references = order_args.grep(String)
+        references = order_args.flat_map do |arg|
+          case arg
+          when String
+            arg
+          when Hash
+            arg.keys
+          end
+        end
         references.map! { |arg| arg =~ /^\W?(\w+)\W?\./ && $1 }.compact!
         references
       end

activerecord/test/cases/relations_test.rb

@@ -1704,6 +1704,26 @@ class RelationTest < ActiveRecord::TestCase
     assert_not_predicate scope, :eager_loading?
   end
 
+  def test_order_triggers_eager_loading
+    scope = Post.includes(:comments).order("comments.label ASC")
+    assert_predicate scope, :eager_loading?
+  end
+
+  def test_order_doesnt_trigger_eager_loading_when_ordering_using_the_owner_table
+    scope = Post.includes(:comments).order("posts.title ASC")
+    assert_not_predicate scope, :eager_loading?
+  end
+
+  def test_order_triggers_eager_loading_when_ordering_using_hash_syntax
+    scope = Post.includes(:comments).order({ "comments.label": :ASC })
+    assert_predicate scope, :eager_loading?
+  end
+
+  def test_order_doesnt_trigger_eager_loading_when_ordering_using_the_owner_table_and_hash_syntax
+    scope = Post.includes(:comments).order({ "posts.title": :ASC })
+    assert_not_predicate scope, :eager_loading?
+  end
+
   def test_automatically_added_where_references
     scope = Post.where(comments: { body: "Bla" })
     assert_equal ["comments"], scope.references_values