Fix typo in method names [ci-skip]

Author: jonathanhefner

activemodel/lib/active_model/dirty.rb

@@ -289,7 +289,7 @@ def changed
       mutations_from_database.changed_attribute_names
     end
 
-    # Dispatch target for {*_changed}[rdoc-label:method-i-2A_changed-3F] attribute methods.
+    # Dispatch target for {*_changed?}[rdoc-label:method-i-2A_changed-3F] attribute methods.
     def attribute_changed?(attr_name, **options)
       mutations_from_database.changed?(attr_name.to_s, **options)
     end
@@ -299,7 +299,7 @@ def attribute_was(attr_name)
       mutations_from_database.original_value(attr_name.to_s)
     end
 
-    # Dispatch target for {*_previously_changed}[rdoc-label:method-i-2A_previously_changed-3F] attribute methods.
+    # Dispatch target for {*_previously_changed?}[rdoc-label:method-i-2A_previously_changed-3F] attribute methods.
     def attribute_previously_changed?(attr_name, **options)
       mutations_before_last_save.changed?(attr_name.to_s, **options)
     end