`MariadbContainerTest` fail in debug mode

From: https://github.com/Kotlin/dataframe/pull/2086

> * **Four `MariadbContainerTest` tests fail on `master`** with `-Pkotlin.dataframe.debug=true` (`read from all tables`, `readAllSqlTables without catalogue…`, `basic test for reading sql tables`, `reading numeric types`). Cause: `tinyblobCol` is typed `java.sql.Blob` but the values are `ByteArray`, tripping the [issue #713](https://github.com/Kotlin/dataframe/issues/713) debug assertion in `DataColumnImpl`. I reproduced this on unmodified `master` with MariaDB 3.5.9 and confirmed it is **pre-existing and unrelated to this PR** — it disappears with debug mode off. Reported here because it is only reachable with Docker plus the debug flag, so it may have gone unnoticed.