MDEV-18874 : Galera test MW-286 causes Mutex = TTASEventMutex<GenericPolicy>]: Assertion `!is_owned()' failed. assertion

MDEV-24649 galera.galera_bf_lock_wait MTR failed with sigabrt: Assertion `!is_ow
ned()' failed in sync0policy.ic on MutexDebug with Mutex = TTASEventMutex<GenericPolicy>

Bug was fixed as part of MDEV-23328, this just adds test cases to
regression set.