MDEV-27966 Assertion `fixed()' failed and Assertion `fixed == 1' failed, both in Item_func_concat::val_str on SELECT after INSERT with collation utf32_bin on utf8_bin table

This problem was earlier fixed by this commit:

> commit 08c7ab40
> Author: Aleksey Midenkov <midenok@gmail.com>
> Date:   Mon Apr 18 12:44:27 2022 +0300
>
>    MDEV-24176 Server crashes after insert in the table with virtual
>    column generated using date_format() and if()

Adding an mtr test only.