fixed dc640ba2 from https://gitee.com/yamila89/docs/pulls/23243

update dialog
Signed-off-by: Nyamila <tianyu55@huawei.com>

zh-cn/application-dev/reference/arkui-ts/ts-methods-custom-dialog-box.md

@@ -108,7 +108,7 @@ struct CustomDialogUser {
     }),
     cancel: this.existApp,
     autoCancel: true,
-    alignment: DialogAlignment.Default,
+    alignment: DialogAlignment.Bottom,
     offset: { dx: 0, dy: -20 },
     gridCount: 4,
     customStyle: false,