refactor(接口测试): 修复mock期望响应为xml格式时xml头无法删除的问题

--bug=1011723
--user=宋天阳
【接口测试】github#11969，https://www.tapd.cn/55049933/s/1126842

frontend/src/business/components/api/definition/components/body/ApiBodyFileUpload.vue

@@ -115,6 +115,10 @@
   }
 
   .upload-item {
+    white-space: nowrap;
+    text-overflow: ellipsis;
+    overflow: hidden;
+    width: 180px;
   }
 
 </style>

frontend/src/business/components/api/definition/components/mock/Components/MockApiResponseBody.vue

@@ -150,7 +150,7 @@ export default {
 
     'body.xmlHeader'() {
       if (!this.body.xmlHeader) {
-        this.body.xmlHeader = 'version="1.0" encoding="UTF-8"';
+        this.body.xmlHeader = '';
       }
     },
   },