RE: pg_upgrade and logical replication

Dear Julien,

I found a cfbot failure on macOS [1]. According to the log,
"SELECT count(*) FROM t2" was executed before synchronization was done.

```
[09:24:21.018](0.132s) not ok 18 - Table t2 should now have 3 rows on the new subscriber
```

With the patch present, wait_for_catchup() is executed after REFRESH, but
it may not be sufficient because it does not check pg_subscription_rel.
wait_for_subscription_sync() seems better for the purpose.


[1]: https://cirrus-ci.com/task/6563827802701824

Best Regards,
Hayato Kuroda
FUJITSU LIMITED