Add missing `attr_name.to_s` in `AttributeMutationTracker`

`attributes` (`values` in `LazyAttributeHash` in `AttributeSet`) has
string keys, not symbols.

Fixes #29665.

1 files changed, 3 insertions, 2 deletions

diff --git a/activerecord/lib/active_record/attribute_mutation_tracker.rb b/activerecord/lib/active_record/attribute_mutation_tracker.rb
index 4de993e169..a01a58f8a5 100644
--- a/activerecord/lib/active_record/attribute_mutation_tracker.rb
+++ b/activerecord/lib/active_record/attribute_mutation_tracker.rb
@@ -26,6 +26,7 @@ module ActiveRecord
     end
 
     def change_to_attribute(attr_name)
+      attr_name = attr_name.to_s
       if changed?(attr_name)
         [attributes[attr_name].original_value, attributes.fetch_value(attr_name)]
       end
@@ -44,7 +45,7 @@ module ActiveRecord
     end
 
     def changed_in_place?(attr_name)
-      attributes[attr_name].changed_in_place?
+      attributes[attr_name.to_s].changed_in_place?
     end
 
     def forget_change(attr_name)
@@ -54,7 +55,7 @@ module ActiveRecord
     end
 
     def original_value(attr_name)
-      attributes[attr_name].original_value
+      attributes[attr_name.to_s].original_value
     end
 
     def force_change(attr_name)