Add classifier and testing for Python 3.12

[markkuleinio]

pynetbox version

v7.3.0

NetBox version

v3.7.0

Feature type

Change to existing functionality

Proposed functionality

Add Python 3.12 in setup.py classifiers and in the test runs.

Use case

Python 3.12 has been out for three months, and the first fix release 3.12.1 is also out already, so let's test against it as well.

External dependencies

No response