fix failed_test_lists none (#33884)

paddle/scripts/paddle_build.sh

@@ -1224,8 +1224,10 @@ set +x
             if [ $need_retry_ut_count -lt $exec_retry_threshold ];then
                 while ( [ $exec_times -lt $retry_time ] )
                     do
+                        set +e
                         retry_unittests_record="$retry_unittests_record$failed_test_lists"
                         failed_test_lists_ult=`echo "${failed_test_lists}" |grep -Po '[^ ].*$'`
+                        set -e
                         if [[ "${exec_times}" == "1" ]];then
                             if [[ "${failed_test_lists}" == "" ]];then
                                 break