Use Ci::Pipeline#merge_request as the merge request for all builds

app/models/ci/build.rb

@@ -591,13 +591,7 @@ module Ci
 
     def merge_request
       strong_memoize(:merge_request) do
-        merge_requests = MergeRequest.includes(:latest_merge_request_diff)
-          .where(source_branch: ref, source_project: pipeline.project)
-          .reorder(iid: :desc)
-
-        merge_requests.find do |merge_request|
-          merge_request.commit_shas.include?(pipeline.sha)
-        end
+        pipeline.all_merge_requests.first
       end
     end
 

changelogs/unreleased/update-ci-build-merge-request.yml

+---
+title: Use Ci::Pipeline#all_merge_requests.first as Ci::Build#merge_request
+merge_request: 27968
+author:
+type: fixed