Update HeidiSQL to v12.8

With MDEV-27009 (resolved 2022-08-10) new collation sequences were made available. The version of HeidiSQL that is bundled with MariaDB can't show the full utf8mb4_uca1400_ai_ci collation in its list of collations. It only shows "uca..." names.
With MDEV-30624 (2023-02-10) the bundled HeidiSQL was updated to its v12.3.
However, HeidiSQL wasn't enhanced to show the full collation name until it's v12.7 (resolved 2024-03-03). Github #1917
This means someone installing the current download of MariaDB v11.5 today can't set collation to the server's default.

The current solution to this is to once again update the bundled HeidiSQL to its current v12.8.

Perhaps a longer-term solution is to avoid a direct bundle but to have the installer retrieve the current production version of HeidiSQL from its repo? A discussion with @ansgarbecker might be in order.

( This is my first post to this Jira, please forgive any breach of local protocol. I set this as a major bug because that was accepted as the setting for the ref'd tickets. It seems to me that an issue with the built-in GUI's ability to specify the correct collation is indeed significant. TY )