Frequent timeouts of the test innodb.innodb_bug38231

The test innodb.innodb_bug38231, which normally executes in some milliseconds, is frequently exceeding the 900-second timeout due to something outside InnoDB.

The first recent failure that I was able to find was for a July 16 change, backdated to May 28. This change is not the culprit, even though the test timed out on 4 different builds of that same change. There is a slightly older change that looks related; maybe it was pushed to the main branch at the same time by serg?

That suspicious change was backported to the 10.11 branch on September 9. Since that time, I can find many failures in 10.11 and 11.4 based development branches. This change has not been merged to the 11.8 branch yet; to my understanding, the merge may be blocked by MDEV-26115.