fix(接口测试): 修复添加场景变量csv文件设置分隔符为;保存失效的缺陷

--bug=1015680 --user=王孝刚
【接口测试】github#16675，首次添加场景变量csv本地文件，设置分隔符为；保存后仍为，非首次正常
https://www.tapd.cn/55049933/s/1220006

frontend/src/business/components/api/automation/scenario/variable/VariableList.vue

@@ -300,7 +300,7 @@ export default {
     addParameters(v) {
       v.id = getUUID();
       if (v.type === 'CSV') {
-        v.delimiter = ",";
+        v.delimiter = v.delimiter ? v.delimiter : ",";
       }
       this.variables.push(v);
       let index = 1;