pgsql: doc: Fix link to SELinux user guide in sepgsql page

doc: Fix link to SELinux user guide in sepgsql page

Reported-by: Anton Voloshin
Discussion: /messages/by-id/15a86d4e-a237-1acd-18a2-fd69730f1ab9@postgrespro.ru
Backpatch-through: 10

Branch
------
REL_13_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/0a75e1186afe58e140cc5eb0f6f0c13f5b7d8c3b

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