fields named serial are incorrectly converted

Likely field name serial is being treated as if it's a serial type https://github.com/dolthub/pg2mysql/blob/main/pg2mysql.pl#L167

```
$ cat test.pgsql
CREATE TABLE public.dcim_device (
id uuid NOT NULL,
created date,
serial character varying(255) NOT NULL,
);

$ perl pg2mysql.pl < test.pgsql
--
-- Generated by pg2mysql
--
set foreign_key_checks = off;
--
DROP DATABASE IF EXISTS public;
CREATE DATABASE public;
CREATE TABLE public.dcim_device (
`id` varchar(36) NOT NULL,
`created` date,
`integer` auto_increment varchar(255) NOT NULL,
);
```

Inspect pg2mysql.pl around line 167, then run the provided test.pgsql input through `perl pg2mysql.pl`. Confirm that a field named serial remains named `serial` with its declared varchar type, rather than becoming an auto-increment integer, and add or update coverage if the repository provides tests.

Written by the indexing model from the issue text.