fix(tabs): 示例文档文案错误 (#3741)

Author: RSS1102

src/tabs/_example-composition/drag-sort.vue

@@ -44,7 +44,7 @@ const panelData = ref([
   {
     value: 'third',
     label: '可拖拽的选项卡3',
-    content: '选项卡2内容',
+    content: '选项卡3内容',
   },
 ]);
 

src/tabs/_example/drag-sort.vue

@@ -43,7 +43,7 @@ export default {
         {
           value: 'third',
           label: '可拖拽的选项卡3',
-          content: '选项卡2内容',
+          content: '选项卡3内容',
         },
       ],
     };