fix: table struct current_timestamp problem

[oatiz]

related: #360

[caiq1nyu]

LGTM,we will review it as soon as possible

[caiq1nyu]

能否提供一下用于复现这个case的来源库的建表语句，以及MySQL版本。关联issue里缺少一些结论细节

[oatiz]

能否提供一下用于复现这个case的来源库的建表语句，以及MySQL版本。关联issue里缺少一些结论细节

MySQL:

docker run --name mysql-5.7 -e MYSQL_ROOT_PASSWORD=123456 -p 33061:3306 -d mysql:5.7.44

sql

create database ape_dts_src;
create database ape_dts_dst;

use ape_dts_src;

CREATE TABLE `current_timestamp_case` (
  `id` bigint(20) NOT NULL AUTO_INCREMENT,
  `key` varchar(255) NOT NULL,
  `value` varchar(5000) NOT NULL,
  `is_deleted` tinyint(4) DEFAULT NULL,
  `created_at` datetime DEFAULT CURRENT_TIMESTAMP,
  `last_updated_at` datetime(6) DEFAULT CURRENT_TIMESTAMP(6) ON UPDATE CURRENT_TIMESTAMP(6),
  PRIMARY KEY (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4;

ape-dts

[extractor]
extract_type=struct
db_type=mysql
url=mysql://root:123456@127.0.0.1:33061?ssl-mode=disabled

[sinker]
sink_type=struct
db_type=mysql
url=mysql://root:123456@127.0.0.1:33061?ssl-mode=disabled

[filter]
do_dbs=ape_dts_src

[router]
db_map=ape_dts_src:ape_dts_dst

[parallelizer]
parallel_type=serial

[pipeline]
buffer_size=100
checkpoint_interval_secs=1