Fix second race condition in 002_archiving.pl with archive_cleanup_command

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