Debian Repo installation is broken

I wanted to install MariaDB 11.8 as described here on Debian 13 (Trixie):

https://mariadb.org/download/?t=repo-config&d=Debian+Linux&v=11.8&r_m=mva

And did not succeed:

root@deb13:~# apt-get install apt-transport-https curl
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
apt-transport-https is already the newest version (3.0.3).
curl is already the newest version (8.14.1-2+deb13u2).
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.

root@deb13:~# mkdir -p /etc/apt/keyrings

root@deb13:~# curl -o /etc/apt/keyrings/mariadb-keyring.pgp 'https://mariadb.org/mariadb_release_signing_key.pgp'
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 6575 100 6575 0 0 30437 0 -::- -::- -::- 30439

root@deb13:~# vi /etc/apt/sources.list.d/mariadb.sources

root@deb13:~# apt update
Hit:1 http://deb.debian.org/debian trixie InRelease
Hit:2 http://deb.debian.org/debian trixie-updates InRelease
Ign:3 https://mirror.mva-n.net/mariadb/repo/11.8/debian debian InRelease
Hit:4 http://deb.debian.org/debian-security trixie-security InRelease
Err:5 https://mirror.mva-n.net/mariadb/repo/11.8/debian debian Release
404 Not Found [IP: 195.65.111.42 443]
Error: The repository 'https://mirror.mva-n.net/mariadb/repo/11.8/debian debian Release' does not have a Release file.
Notice: Updating from such a repository can't be done securely, and is therefore disabled by default.
Notice: See apt-secure(8) manpage for repository creation and user configuration details.

This problem also happened on Debian 12. It works without problems on Ubuntu 24.04. It also happened with older MariaDB releases...