## Problem
The pg_repack test can be flaky due to unpredictable `NOTICE` messages
about waiting for some processes.
E.g.,
```
INFO: repacking table "public.issue3_2"
+NOTICE: Waiting for 1 transactions to finish. First PID: 427
```
## Summary of changes
The `client_min_messages` set to `warning` for the regression tests.