MDEV-27966 Assertion `fixed()' failed and Assertion `fixed == 1' failed, both...

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.

mysql-test/suite/vcol/r/vcol_utf32.result

+#
+# 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
+#
+SET NAMES utf8mb3;
+SET sql_mode='';
+CREATE TABLE t (c1 INT,c2 CHAR AS (CONCAT ('',DAYNAME ('')))) COLLATE utf8_bin ENGINE=InnoDB;
+Warnings:
+Warning	1286	Unknown storage engine 'InnoDB'
+Warning	1266	Using storage engine MyISAM for table 't'
+INSERT INTO t VALUES (0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0);
+Warnings:
+Warning	1906	The value specified for generated column 'c2' in table 't' has been ignored
+Warning	1292	Incorrect datetime value: ''
+Warning	1906	The value specified for generated column 'c2' in table 't' has been ignored
+Warning	1292	Incorrect datetime value: ''
+Warning	1906	The value specified for generated column 'c2' in table 't' has been ignored
+Warning	1292	Incorrect datetime value: ''
+Warning	1906	The value specified for generated column 'c2' in table 't' has been ignored
+Warning	1292	Incorrect datetime value: ''
+Warning	1906	The value specified for generated column 'c2' in table 't' has been ignored
+Warning	1292	Incorrect datetime value: ''
+Warning	1906	The value specified for generated column 'c2' in table 't' has been ignored
+Warning	1292	Incorrect datetime value: ''
+Warning	1906	The value specified for generated column 'c2' in table 't' has been ignored
+Warning	1292	Incorrect datetime value: ''
+Warning	1906	The value specified for generated column 'c2' in table 't' has been ignored
+Warning	1292	Incorrect datetime value: ''
+Warning	1906	The value specified for generated column 'c2' in table 't' has been ignored
+Warning	1292	Incorrect datetime value: ''
+SET collation_connection='utf32_bin';
+INSERT INTO t VALUES (0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0);
+ERROR HY000: Illegal mix of collations (utf8_bin,COERCIBLE) and (utf32_bin,COERCIBLE) for operation 'concat'
+SELECT * FROM t;
+ERROR HY000: Illegal mix of collations (utf8_bin,COERCIBLE) and (utf32_bin,COERCIBLE) for operation 'concat'
+DROP TABLE t;
+SET sql_mode=DEFAULT;
+SET NAMES utf8mb3;

mysql-test/suite/vcol/t/vcol_utf32.test

+--source include/have_utf32.inc
+
+--echo #
+--echo # 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
+--echo #
+
+SET NAMES utf8mb3;
+SET sql_mode='';
+CREATE TABLE t (c1 INT,c2 CHAR AS (CONCAT ('',DAYNAME ('')))) COLLATE utf8_bin ENGINE=InnoDB;
+INSERT INTO t VALUES (0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0);
+SET collation_connection='utf32_bin';
+--error ER_CANT_AGGREGATE_2COLLATIONS
+INSERT INTO t VALUES (0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0),(0,0);
+--error ER_CANT_AGGREGATE_2COLLATIONS
+SELECT * FROM t;
+DROP TABLE t;
+SET sql_mode=DEFAULT;
+SET NAMES utf8mb3;