Merge branch 'use-cheap-operation-for-ci-pipeline-all_merge_requests' into 'master'

Use cheap operation for `Ci::Pipeline#all_merge_requests`

Closes #54907

See merge request gitlab-org/gitlab-ce!24115

app/models/ci/pipeline.rb

@@ -635,7 +635,7 @@ module Ci
     def all_merge_requests
       @all_merge_requests ||=
         if merge_request?
-          project.merge_requests.where(id: merge_request.id)
+          project.merge_requests.where(id: merge_request_id)
         else
           project.merge_requests.where(source_branch: ref)
         end