pgsql: Doc: fix missing comma at the end of a line.

Doc: fix missing comma at the end of a line.

Backpatch to 17, where the line was added.

Reported by Noboru Saito while he was working on translating the file
into Japanese.

Discussion: https://postgr.es/m/20250417.203047.1321297410457834775.ishii%40postgresql.org
Reported-by: Noboru Saito <noborusai@gmail.com>
Reviewed-by: Daniel Gustafs <daniel@yesql.se>
Backpatch-through: 17

Branch
------
REL_17_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/4a0650d359c5981270039eeb634c3b7427aa0af5

Modified Files
--------------
doc/src/sgml/libpq.sgml | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)