pgsql: pg_test_timing: fix unit in backward-clock warning

pg_test_timing: fix unit in backward-clock warning

pg_test_timing reports timing differences in nanoseconds in master, and
in microseconds in v14 through v18, but previously the backward-clock
warning incorrectly labeled the value as milliseconds.

This commit fixes the warning message to use "ns" in master and
"us" in v14 through v18, matching the actual unit being reported.

Backpatch to all supported versions.

Author: Chao Li <lic(at)highgo(dot)com>
Reviewed-by: Lukas Fittl <lukas(at)fittl(dot)com>
Reviewed-by: Xiaopeng Wang <wxp_728(at)163(dot)com>
Reviewed-by: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
Discussion: https://postgr.es/m/F780CEEB-A237-4302-9F55-60E9D8B6533D@gmail.com
Backpatch-through: 14

Branch
------
REL_17_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/1fdf1c63744c301bef44bf1723ba44961a4c4af5

Modified Files
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src/bin/pg_test_timing/pg_test_timing.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)