fix(接口定义): 优化场景变量类型默认值 (#15807)

--bug=1014897 --user=王孝刚 【接口测试】github#15806，场景变量，没有默认类型，点击添加时建议给个提示
https://www.tapd.cn/55049933/s/1202295

Co-authored-by: wxg0103 <727495428@qq.com>

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

@@ -169,10 +169,7 @@ import {REQUEST_HEADERS} from "@/common/js/constants";
 
 import MsTable from "@/business/components/common/components/table/MsTable";
 import MsTableColumn from "@/business/components/common/components/table/MsTableColumn";
-import {
-  getCustomTableWidth,
-  getCustomTableHeader
-} from "@/common/js/tableUtils";
+import {getCustomTableHeader, getCustomTableWidth} from "@/common/js/tableUtils";
 
 const jsondiffpatch = require('jsondiffpatch');
 
@@ -218,7 +215,7 @@ export default {
       total: 0,
       headerSuggestions: REQUEST_HEADERS,
       disabled: false,
-      selectType: "",
+      selectType: "CONSTANT",
       showDelete: false,
       tableHeaderKey: "VARIABLE_LIST_TABLE",
       fields: getCustomTableHeader('VARIABLE_LIST_TABLE'),