mariadb-10.4.11: Client authentication fails: ERROR 1698 (28000): Access denied for user 'root'@'localhost'

One of the tests fails on authentication error when upgrading from mariadb-10.3 to mariadb-10.4.

Here is the bug report on fedora's bugzilla, for better explanation please read it. https://bugzilla.redhat.com/show_bug.cgi?id=1796106

Execution of command (as user lukas) mariadb -S /tmp/t/tmp/mysql.sock ends with: "Client authentication fails: ERROR 1698 (28000): Access denied for user 'root'@'localhost'." It somehow changed the user to root, because if you run the command with the option --user $USER it starts to work.

I would be really grateful, if you could help me with a solution or give me some tips what could be wrong. Big question for me is why does the mariadb -S /tmp/t/tmp/mysql.sock command tries to access the root@localhost, when the user is someone else.