This fixes the Postgres unit tests for Django 4.1 and 4.2 (mostly).

Django 4.1 changed primary key definitions for models, which this test

now conditionalizes, to go from serial to integer types. As part of

this, it also dropped some table-rebuilding logic that tried to restore

the serial indexes, which are no longer needed.
Django 4.2 inherits these fixes, but breaks in other ways due to new

model meta attributes that we don't currently support. These will be

introduced next.

Ran unit tests for Django 3.2 through 4.2 for SQLite, MySQL, and

Postgres. All unit tests pass, except for the failures mentioned for 4.2.