fix alter table test

Author: elianddb

enginetest/queries/alter_table_queries.go

@@ -1051,13 +1051,13 @@ var AlterTableScripts = []ScriptTest{
 		Name: "alter table supports non-escaped \\Z",
 		SetUpScript: []string{
 			"create table t (i int);",
-			`alter table t modify column i int comment "ctrlz \\Z \\Z"`,
+			`alter table t modify column i int comment "ctrlz \Z \\Z"`,
 		},
 		Assertions: []ScriptTestAssertion{
 			{
 				Query: "show create table t",
 				Expected: []sql.Row{{"t", "CREATE TABLE `t` (\n" +
-					"  `i` int COMMENT 'ctrlz \\Z \\Z'\n" +
+					"  `i` int COMMENT 'ctrlz \x1A \\\\Z'\n" +
 					") ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_bin"}},
 			},
 		},