pgsql: test_custom_stats: Stabilize test for counters

test_custom_stats: Stabilize test for counters

After 44539786b82, variable-sized stats updates are batched in one
backend. A later safe_psql() can check the counters before that backend
has finished flushing its pending stats during shutdown, so force a
flush before checking them.

This is only needed before this report check because
test_custom_stats_var_update() uses pgstat_prep_pending_entry(), leaving
counter updates as backend-local pending stats.

Per buildfarm member mamba. This could be reproduced locally by slowing
down pgstat_shutdown_hook().

Reported-by: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Author: Sami Imseih <samimseih(dot)pg(at)gmail(dot)com>
Discussion: https://postgr.es/m/193326.1792282194@sss.pgh.pa.us

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/8afc886831bc629e524cc7185b2fdc0092aecc93

Modified Files
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src/test/modules/test_custom_stats/t/001_custom_stats.pl | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)