[NEOS-1742] Add integration test that ensures PG create statements don't return dupes

[nickzelei]

We discovered an issue where a create table statement returned duplicate columns.

This was caused by a serial value returning a non-sequence record in our linked sequence CTE.

This happened because of an index that was composite and referenced the column.

We fixed it but should add a test.

Might also be worth handling the de-duping at the API layer too?

The PR of the original fix is here: #3244

_{From SyncLinear.com | NEOS-1742}