Improve performance of project issues API

Remove unneeded preloading of notes. This can be really expensive
because it is not unusual for issues to have lots of notes.

Changelog: performance
MR: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/60981

app/models/issue.rb

@@ -123,7 +123,7 @@ class Issue < ApplicationRecord
   scope :with_prometheus_alert_events, -> { joins(:issues_prometheus_alert_events) }
   scope :with_self_managed_prometheus_alert_events, -> { joins(:issues_self_managed_prometheus_alert_events) }
   scope :with_api_entity_associations, -> {
-    preload(:timelogs, :closed_by, :assignees, :author, :notes, :labels,
+    preload(:timelogs, :closed_by, :assignees, :author, :labels,
       milestone: { project: [:route, { namespace: :route }] },
       project: [:route, { namespace: :route }])
   }

changelogs/unreleased/211373-remove-notes-preload-in-issues-api.yml

+---
+title: Improve performance of project issues API
+merge_request: 60981
+author:
+type: performance

spec/requests/api/issues/get_project_issues_spec.rb

@@ -186,7 +186,7 @@ RSpec.describe API::Issues do
     it 'avoids N+1 queries' do
       get api("/projects/#{project.id}/issues", user)
 
-      create_list(:issue, 3, project: project, closed_by: user)
+      issues = create_list(:issue, 3, project: project, closed_by: user)
 
       control_count = ActiveRecord::QueryRecorder.new(skip_cached: false) do
         get api("/projects/#{project.id}/issues", user)
@@ -195,6 +195,10 @@ RSpec.describe API::Issues do
       milestone = create(:milestone, project: project)
       create(:issue, project: project, milestone: milestone, closed_by: create(:user))
 
+      create(:note_on_issue, project: project, noteable: issues[0])
+      create(:note_on_issue, project: project, noteable: issues[0])
+      create(:note_on_issue, project: project, noteable: issues[1])
+
       expect do
         get api("/projects/#{project.id}/issues", user)
       end.not_to exceed_all_query_limit(control_count)