As part of
MDEV-12288, a parameter of trx_undo_commit_cleanup() was accidentally always passed as bool noredo=true.
The impact of this should be that some undo log pages may not be correctly freed if the server is killed and crash recovery will be performed. Similarly, if mariabackup --backup is being executed concurrently with user transaction commits, it could happen that some undo log pages in the backup will never be marked as free for reuse.
As far as I can tell, this bug should not have any user-visible impact other than some undo pages being wasted. I found the bug when working on code refactoring.