RE: Slow catchup of 2PC (twophase) transactions on replica in LR

> Dear hackers,
> 
> I found that v12 patch set could not be accepted by the cfbot. PSA new version.

To make others more trackable, I shared changes just in case. All failures were occurred
on the pg_dump code. I added an attribute in pg_subscription and modified pg_dump code,
but it was wrong. A constructed SQL became incomplete. I.e., in [1]: 

```
pg_dump: error: query failed: ERROR:  syntax error at or near "."
LINE 15:  s.subforcealter
           ^
pg_dump: detail: Query was: SELECT s.tableoid, s.oid, s.subname,
 s.subowner,
 s.subconninfo, s.subslotname, s.subsynccommit,
 s.subpublications,
 s.subbinary,
 s.substream,
 s.subtwophasestate,
 s.subdisableonerr,
 s.subpasswordrequired,
 s.subrunasowner,
 s.suborigin,
 NULL AS suboriginremotelsn,
 false AS subenabled,
 s.subfailover
 s.subforcealter
FROM pg_subscription s
WHERE s.subdbid = (SELECT oid FROM pg_database
                   WHERE datname = current_database())
```

Based on that I just added a comma in 0004 patch.

[1]: https://cirrus-ci.com/task/6710166165389312

Best Regards,
Hayato Kuroda
FUJITSU LIMITED
https://www.fujitsu.com/