pgsql: Fix typo in comment

Fix typo in comment

Commit 98e675ed7af accidentally mistyped IDENTIFY_SYSTEM as
IDENTIFY_SERVER. Backpatch to all supported branches.

Reported-by: Alexander Lakhin <exclusion@gmail.com>
Discussion: https://postgr.es/m/68138521-5345-8780-4390-1474afdcba1f@gmail.com

Branch
------
REL_14_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/d86038bd4d81ebd7dda60f5458476710108ec0a3

Modified Files
--------------
src/backend/replication/libpqwalreceiver/libpqwalreceiver.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)