Merge pull request #12224 from nextcloud/jtr/fix/admin-release-notes-mariadb-10.5

fix(upgrade_to_30): Note the drop of MariaDB 10.5 support

Author: susnux

admin_manual/release_notes/upgrade_to_30.rst

@@ -8,6 +8,7 @@ System requirements
 * PHP 8.1 is now deprecated but still supported.
 * PHP 8.0 is no longer supported.
 * PostgreSQL 9.4 is no longer supported.
+* MariaDB 10.3 and 10.5 are no longer supported.
 
 Web server configuration
 ------------------------