* Wait for all computes (except one) to complete before proceeding with
the single compute.
* It previously waited for too few seconds. As the test is randomized, it was
not failing all the time, but only in specific unlucky cases.
E.g. when there were no successfuly queries by concurrent computes,
and the single node had big timeouts and spent lots of time making the
transaction.
See https://github.com/neondatabase/neon/runs/7234456482?check_suite_focus=true
(around line 980).
* Wait for exactly one extra transaction by the single compute.
1b6a80a38f