Iterate over all records in Transaction#before_commit_records

Follow up to rails@6175f73:
we need to iterate over all records instead of the unique records when finding
callback candidates.

Author: adrianna-chang-shopify

activerecord/lib/active_record/connection_adapters/abstract/transaction.rb

@@ -173,7 +173,7 @@ def before_commit_records
         if @run_commit_callbacks
           ite = unique_records
 
-          instances_to_run_callbacks_on = ite.each_with_object({}) do |record, candidates|
+          instances_to_run_callbacks_on = records.each_with_object({}) do |record, candidates|
             candidates[record] = record
           end