Set proper query limit for pipeline serializer

This limit is (and already was) different in compare to CE
version, bumping this now to reflect recent change introduced by
gitlab-ce!18735.

spec/serializers/pipeline_serializer_spec.rb

@@ -139,7 +139,7 @@ describe PipelineSerializer do
           # pipeline. With the same ref this check is cached but if refs are
           # different then there is an extra query per ref
           # https://gitlab.com/gitlab-org/gitlab-ce/issues/46368
-          expect(recorded.count).to be_within(1).of(51)
+          expect(recorded.count).to be_within(1).of(56)
           expect(recorded.cached_count).to eq(0)
         end
       end