pgsql: doc PG 18 relnotes: fix libpq wording

doc PG 18 relnotes: fix libpq wording

Reported-by: Jelte Fennema-Nio

Discussion: /messages/by-id/CAGECzQT4804OLOP+nDBxDpMw3Soq=g+fKOE7NryBHggy4GgEcg@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/a675149e87706d01e4007150a0124b89bdef08be

Modified Files
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doc/src/sgml/release-18.sgml | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)