seems not able to use arguments

Author: ETOgaosion

tests/e2e/run_ppo_trainer_megatron.sh

@@ -75,7 +75,7 @@ if [ $SKIP_SAVE_HF_MODEL -eq 1 ]; then
     CHECKPOINT_CONTENTS=['model','optimizer','extra']
 fi
 
-ENGINES=${ENGINES:-("vllm" "sglang_async")}
+ENGINES=("vllm" "sglang_async")
 
 exp_name="$(basename "${MODEL_ID,,}")-megatron-gsm8k-minimal"