Use RequestStore on MR show.json query count spec

spec/controllers/projects/merge_requests_controller_spec.rb

@@ -121,13 +121,18 @@ describe Projects::MergeRequestsController do
 
       context 'number of queries' do
         it 'verifies number of queries' do
+          RequestStore.begin!
+
           # pre-create objects
           merge_request
 
           recorded = ActiveRecord::QueryRecorder.new { go(format: :json) }
 
-          expect(recorded.count).to be_within(5).of(50)
+          expect(recorded.count).to be_within(5).of(30)
           expect(recorded.cached_count).to eq(0)
+
+          RequestStore.end!
+          RequestStore.clear!
         end
       end
     end