Make diff discussion more reliable

app/models/merge_request.rb

@@ -861,9 +861,11 @@ class MergeRequest < ActiveRecord::Base
       paths: paths
     )
-    active_diff_notes.each do |note|
-      service.execute(note)
-      Gitlab::Timeless.timeless(note, &:save)
+    transaction do
+      active_diff_notes.each do |note|
+        service.execute(note)
+        Gitlab::Timeless.timeless(note, &:save)
+      end
     end
   end

changelogs/unreleased/fix_broken_diff_discussions.yml

+---
+title: Make MR-review-discussions more reliable
+merge_request:
+author: