lower_case_table_names=2 breaks mixed-case schema name queries in I_S.routines

When using lower_case_table_names=2 and a mixed-case schema name, WHERE clauses on information_schema.routines.routine_schema no longer perform case-insensitive matching properly.

This previously worked, e.g. here's the behavior in MariaDB 11.7.2 and all pre-May releases of MariaDB (and all versions of MySQL):

MariaDB [(none)]> CREATE DATABASE FooBar;

Query OK, 1 row affected (0.029 sec)

MariaDB [(none)]> CREATE PROCEDURE FooBar.testing() SELECT 1;

Query OK, 0 rows affected (0.046 sec)

MariaDB [(none)]> SELECT routine_schema, routine_type, routine_name FROM information_schema.routines WHERE routine_schema = 'FooBar';

+----------------+--------------+--------------+

| routine_schema | routine_type | routine_name |

+----------------+--------------+--------------+

| foobar         | PROCEDURE    | testing      |

+----------------+--------------+--------------+

1 row in set (0.002 sec)

In comparison, here's MariaDB 11.8, note that the same query returns no rows:

MariaDB [(none)]> CREATE DATABASE FooBar;

Query OK, 1 row affected (0.021 sec)

MariaDB [(none)]> CREATE PROCEDURE FooBar.testing() SELECT 1;

Query OK, 0 rows affected (0.045 sec)

MariaDB [(none)]> SELECT routine_schema, routine_type, routine_name FROM information_schema.routines WHERE routine_schema = 'FooBar';

Empty set (0.002 sec)

As a workaround, applying a case-insensitive COLLATE clause fixes the query, but I don't think that should normally be necessary here.

As far as I can see, this only seems to affect routines. The behavior of tables, views, triggers, and events are unchanged, in terms of information_schema WHERE clauses on a mixed-case schema name.

This might also affect `mysqldump` and other tools, but I haven't tested.

I'm 99% sure this is some unexpected side-effect of MDEV-14432, as the impacted versions seem to line up with May 2025 releases, and I don't see any other recent lower_case_table_name=2 changes. But after staring at sql_show.cc and https://github.com/MariaDB/server/commit/ddd5ba3 the exact cause isn't clear to me.