docs: fix Postgre DSN sample

See "Table 33.1. SSL Mode Descriptions"
in https://www.postgresql.org/docs/12/libpq-ssl.html#LIBPQ-SSL-PROTECTION

user_guide_src/source/database/configuration/010.php

@@ -10,7 +10,7 @@ class Database extends Config
 
     // Postgre
     public array $default = [
-        'DSN' => 'Postgre://username:password@hostname:5432/database?charset=utf8&connect_timeout=5&sslmode=1',
+        'DSN' => 'Postgre://username:password@hostname:5432/database?charset=utf8&connect_timeout=5&sslmode=require',
         // ...
     ];