fix: migrator error of gorm on second run

[WaferJay]

See go-gorm/gorm#5409.

The solution is referenced from go-gorm/gorm#5409 (comment)

db, err := gorm.Open(postgres.New(postgres.Config{
  DSN: "host=localhost user=gorm password=gorm dbname=gorm port=9920 sslmode=disable TimeZone=Asia/Shanghai", // data source name, refer https://github.com/jackc/pgx
  PreferSimpleProtocol: true, // disables implicit prepared statement usage. By default pgx automatically uses the extended protocol
}), &gorm.Config{})

Have a nice day. :-)

[tiagorlampert]

this constant can now be removed

[tiagorlampert]

thanks @WaferJay