s1ap: fix s1ap test after the changes to S1 setup request

srsenb/test/s1ap/s1ap_test.cc

@@ -225,6 +225,9 @@ void test_s1ap_erab_setup(test_event event)
   args.enb_name      = "srsenb01";
 
   TESTASSERT(s1ap_obj.init(args, &rrc) == SRSRAN_SUCCESS);
+  // The S1 Setup Procedure will call `notify_background_task_result`
+  // which we need to manually trigger with `run_next_task()`
+  task_sched.run_next_task();
 
   run_s1_setup(s1ap_obj, mme);
   add_rnti(s1ap_obj, mme);