reduce threads number to avoid hang in CI

test=develop

paddle/fluid/inference/tests/api/analyzer_rnn1_tester.cc

@@ -283,7 +283,7 @@ TEST(Analyzer_rnn1, multi_thread) {
   std::vector<std::vector<PaddleTensor>> input_slots_all;
   SetInput(&input_slots_all);
   TestPrediction(reinterpret_cast<const PaddlePredictor::Config *>(&cfg),
-                 input_slots_all, &outputs, 4 /* multi_thread */);
+                 input_slots_all, &outputs, 2 /* multi_thread */);
 }
 
 // Validate that the AnalysisPredictor + ZeroCopyTensor really works by testing