chore(demo): 修正表单增删示例类型错误

src/views/demo/form/AppendForm.vue

@@ -7,7 +7,7 @@
           <Button class="ml-2" v-if="Number(field) === 0" @click="batchAdd">
             批量添加表单配置
           </Button>
-          <Button v-if="field > 0" @click="del(field)">-</Button>
+          <Button v-if="Number(field) > 0" @click="() => del(field)">-</Button>
         </template>
       </BasicForm>
     </CollapseContainer>
@@ -122,7 +122,7 @@
         n.value++;
       }
 
-      function del(field) {
+      function del(field: string) {
         removeSchemaByField([`field${field}a`, `field${field}b`, `${field}`]);
         n.value--;
       }