Fix second race condition in 002_archiving.pl with archive_cleanup_command

Checking the execution of archive_cleanup_command on a standby requires
a valid checkpoint coming from its primary, but the logic did not check
that the standby replayed up to the point of the checkpoint, causing the
test checking for the execution of archive_cleanup_command to fail.
This race was more visible in slow environments.

Issue introduced in 46dea24, so no backpatch is needed.

Author: Tom Lane
Discussion: https://postgr.es/m/4015413.1649454951@sss.pgh.pa.us

Author: michaelpq

src/test/recovery/t/002_archiving.pl

@@ -46,13 +46,16 @@
 # Create some content on primary
 $node_primary->safe_psql('postgres',
 	"CREATE TABLE tab_int AS SELECT generate_series(1,1000) AS a");
-my $current_lsn =
-  $node_primary->safe_psql('postgres', "SELECT pg_current_wal_lsn();");
 
 # Note the presence of this checkpoint for the archive_cleanup_command
 # check done below, before switching to a new segment.
 $node_primary->safe_psql('postgres', "CHECKPOINT");
 
+# Done after the checkpoint to ensure that it is replayed on the standby,
+# for archive_cleanup_command.
+my $current_lsn =
+  $node_primary->safe_psql('postgres', "SELECT pg_current_wal_lsn();");
+
 # Force archiving of WAL file to make it present on primary
 $node_primary->safe_psql('postgres', "SELECT pg_switch_wal()");