Server with wsrep enabled doesn't respect lock wait timeouts under FLUSH TABLE WITH READ LOCK

Note: might be related to MDEV-22051. The test case is similar, but the one in MDEV-22051 shows what happens if DDL is attempted in the thread holding the lock, while this one – what happens if DDL is attempted concurrently with the lock.

--source include/galera_cluster.inc

--source include/have_innodb.inc

FLUSH TABLES WITH READ LOCK;

--connect (con1,localhost,root,,)

SET lock_wait_timeout= 1;

--error ER_LOCK_WAIT_TIMEOUT

CREATE TABLE t1 (a INT) ENGINE=InnoDB;

The expected result is that after 1 second the CREATE attempt fails with a timeout which is set for the session.. Instead, the statement hangs seemingly forever.

Reproducible on 10.1-10.5, debug and non-debug alike.
Not reproducible if wsrep is disabled.