pgsql: Improve recovery test 046_checkpoint_logical_slot

Improve recovery test 046_checkpoint_logical_slot

This commit improves 046_checkpoint_logical_slot in two aspects:
- Add one pg_logical_emit_message() call to force the creation of a record
that spawns across two pages.
- Make the logic wait for the checkpoint completion.

Discussion: https://postgr.es/m/CALDaNm34m36PDHzsU_GdcNXU0gLTfFY5rzh9GSQv%3Dw6B%2BQVNRQ%40mail.gmail.com
Author: Alexander Korotkov <akorotkov(at)postgresql(dot)org>
Co-authored-by: Hayato Kuroda <kuroda(dot)hayato(at)fujitsu(dot)com>
Reviewed-by: Michael Paquier <michael(at)paquier(dot)xyz>

Branch
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REL_17_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/6aefde2a2db826f363891e1cc1157f22a6c30707

Modified Files
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src/test/recovery/t/046_checkpoint_logical_slot.pl | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)