not support xengine，if the default engine is xengine, gh-ost occurs: ERROR Error 1105: Unsupported collation on string indexed column hint

**root cause is xengine is not support ascii CHARACTER**
mysql> CREATE TABLE `_test_26_ghc` ( `id` bigint(20) NOT NULL AUTO_INCREMENT, `last_update` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP, `hint` varchar(64) CHARACTER SET ascii NOT NULL, `value` varchar(4096) CHARACTER SET ascii NOT NULL, PRIMARY KEY (`id`), UNIQUE KEY `hint_uidx` (`hint`) ) ENGINE=xengine AUTO_INCREMENT=256 DEFAULT CHARSET=utf8mb4;
ERROR 1105 (HY000): Unsupported collation on string indexed column hint. Consider change to other collation (binary, gbk_bin, gbk_chinese_ci, latin1_bin, utf8_bin, utf8_general_ci, utf8mb4_0900_ai_ci, utf8mb4_bin, utf8mb4_general_ci).
mysql>

**errors:**
2025-09-28 15:13:46 INFO starting gh-ost 1.1.4
2025-09-28 15:13:46 INFO Migrating `sbtest`.`test_26`
2025-09-28 15:13:46 INFO inspector connection validated on xxxxx:3306
2025-09-28 15:13:46 INFO User has REPLICATION CLIENT, REPLICATION SLAVE privileges, and has ALL privileges on `sbtest`.*
2025-09-28 15:13:46 INFO binary logs validated on xxxxx:3306
2025-09-28 15:13:46 INFO Inspector initiated on xxxxx:3306, version 8.0.13
2025-09-28 15:13:46 INFO Table found. Engine=XENGINE
2025-09-28 15:13:46 INFO Estimated number of rows via EXPLAIN: 20
2025-09-28 15:13:46 INFO Master forced to be xxxxx:3306
2025-09-28 15:13:46 INFO log_slave_updates validated on xxxxx:3306
2025-09-28 15:13:46 INFO streamer connection validated on xxxxx:3306
[2025/09/28 15:13:46] [info] binlogsyncer.go:133 create BinlogSyncer with config {99999 mysql xxxxx 3306 dba false false false UTC true 0 0s 0s 0 false}
2025-09-28 15:13:46 INFO Connecting binlog streamer at mysql-bin.000005:1014
[2025/09/28 15:13:46] [info] binlogsyncer.go:354 begin to sync binlog from position (mysql-bin.000005, 1014)
[2025/09/28 15:13:46] [info] binlogsyncer.go:203 register slave for master server xxxxx:3306
[2025/09/28 15:13:46] [info] binlogsyncer.go:723 rotate to (mysql-bin.000005, 1014)
2025-09-28 15:13:46 INFO rotate to next log from mysql-bin.000005:0 to mysql-bin.000005
2025-09-28 15:13:46 INFO applier connection validated on xxxxx:3306
2025-09-28 15:13:46 INFO applier connection validated on xxxxx:3306
2025-09-28 15:13:46 INFO will use time_zone='+08:00' on applier
2025-09-28 15:13:46 INFO Examining table structure on applier
2025-09-28 15:13:46 INFO Applier initiated on xxxxx:3306, version 8.0.13
2025-09-28 15:13:46 INFO Dropping table `sbtest`.`_test_26_gho`
2025-09-28 15:13:46 INFO Table dropped
2025-09-28 15:13:46 INFO Dropping table `sbtest`.`_test_26_ghc`
2025-09-28 15:13:46 INFO Table dropped
2025-09-28 15:13:46 INFO Creating changelog table `sbtest`.`_test_26_ghc`
2025-09-28 15:13:46 ERROR Error 1105: Unsupported collation on string indexed column hint. Consider change to other collation (binary, gbk_bin, gbk_chinese_ci, latin1_bin, utf8_bin, utf8_general_ci, utf8mb4_0900_ai_ci, utf8mb4_bin, utf8mb4_general_ci).
2025-09-28 15:13:46 ERROR Unable to create changelog table, see further error details. Perhaps a previous migration failed without dropping the table? OR is there a running migration? Bailing out
2025-09-28 15:13:46 INFO Tearing down inspector
2025-09-28 15:13:46 INFO Tearing down applier
2025-09-28 15:13:46 INFO Tearing down streamer
2025-09-28 15:13:46 FATAL Error 1105: Unsupported collation on string indexed column hint. Consider change to other collation (binary, gbk_bin, gbk_chinese_ci, latin1_bin, utf8_bin, utf8_general_ci, utf8mb4_0900_ai_ci, utf8mb4_bin, utf8mb4_general_ci).