Update PostgreSQL documentation (18.3)

Author: simon04

lib/docs/scrapers/postgresql.rb

@@ -57,7 +57,7 @@ class Postgresql < UrlScraper
     HTML
 
     version '18' do
-      self.release = '18.2'
+      self.release = '18.3'
       self.base_url = "https://www.postgresql.org/docs/#{version}/"
     end