Fix backward not being run in unit test

unit_tests/scheduler/Test_Scheduler.cpp

@@ -436,6 +436,7 @@ TEST_CASE("[cpu/scheduler] SequentialScheduler(backward)", "[scheduler][backward
     // implem already set to default
     auto myProd = Producer(inputTensor, "prod");
     myProd -> addChild(gv);
+    gv->add(myProd);
     gv -> compile("cpu", DataType::Float32);
 
     SequentialScheduler scheduler(gv);