Fix N+1 problem for notes association

Follow-up for https://gitlab.com/gitlab-org/gitlab/-/issues/347407

In previous MR I added a permission verification when user requests
the list of participants. But it increased the number of db queries.

I found that notes association does not preload project object and
that generates additional queries.

Changelog: fixed

app/models/concerns/issuable.rb

@@ -61,6 +61,11 @@ def award_emojis_loaded?
         # We check first if we're loaded to not load unnecessarily.
         loaded? && to_a.all? { |note| note.association(:award_emoji).loaded? }
       end
+
+      def projects_loaded?
+        # We check first if we're loaded to not load unnecessarily.
+        loaded? && to_a.all? { |note| note.association(:project).loaded? }
+      end
     end
 
     has_many :note_authors, -> { distinct }, through: :notes, source: :author
@@ -524,6 +529,7 @@ def notes_with_associations
     includes = []
     includes << :author unless notes.authors_loaded?
     includes << :award_emoji unless notes.award_emojis_loaded?
+    includes << :project unless notes.projects_loaded?
 
     if includes.any?
       notes.includes(includes)

spec/graphql/resolvers/users/participants_resolver_spec.rb

@@ -49,6 +49,19 @@
       it 'returns all participants for this user' do
         is_expected.to match_array([issue.author, note.author])
       end
+
+      it 'does not execute N+1 for project relation' do
+        query = -> { resolve(described_class, args: {}, ctx: { current_user: current_user }, obj: issue)&.items }
+
+        # warm-up
+        query.call
+
+        control_count = ActiveRecord::QueryRecorder.new { query.call }
+
+        create(:note, :confidential, project: project, noteable: issue, author: create(:user))
+
+        expect { query.call }.not_to exceed_query_limit(control_count)
+      end
     end
   end
 end