Fix instability in subscription regression test

Hi,

I noticed BF member wrasse failed in 028_row_filter.pl.

# Failed test 'check publish_via_partition_root behavior'
# at t/028_row_filter.pl line 669.
# got: ''
# expected: '1|100
# ...

Log:
2022-06-23 11:27:42.387 CEST [20589:3] 028_row_filter.pl LOG: statement: ALTER SUBSCRIPTION tap_sub REFRESH PUBLICATION WITH (copy_data = true)
2022-06-23 11:27:42.470 CEST [20589:4] 028_row_filter.pl LOG: disconnection: session time: 0:00:00.098 user=nm database=postgres host=[local]
2022-06-23 11:27:42.611 CEST [20593:1] LOG: logical replication table synchronization worker for subscription "tap_sub", table "tab_rowfilter_partitioned" has started
...
2022-06-23 11:27:43.197 CEST [20610:3] 028_row_filter.pl LOG: statement: SELECT a, b FROM tab_rowfilter_partitioned ORDER BY 1, 2
...
2022-06-23 11:27:43.689 CEST [20593:2] LOG: logical replication table synchronization worker for subscription "tap_sub", table "tab_rowfilter_partitioned" has finished

From the Log, I can see it query the target table before the table sync is
over. So, I think the reason is that we didn't wait for table sync to
finish after refreshing the publication. Sorry for not catching that
ealier. Here is a patch to fix it.

Best regards,
Hou zj