UTF-8 Problem in user group separation

[EinHoerner]

Steps to reproduce

1. Install Nexcloud with saml APP
2. Connect SAML App
3. Use group attributes with UTF8 charakter like 'ü','ß'

Expected behaviour

Group names with UTF-8 characters should be stored and displayed correctly.
Separation should work exactly like with ASCII names.

Actual behaviour

When using group separation that involves group names with UTF-8 characters (e.g. Schüler), the system does not handle them correctly. The group names with UTF8 character become blank after the user logs in and delete all other group names. This is new since 7.0.0

Server configuration

Web server: Linux 6.8.0-60-generic x86_64

Database: MySQL 10

PHP version: 8.3

Nextcloud version: Nextcloud Hub 9 (30.0.12)