Failure to build in Python <= 3.8

[jphickey]

Describe the bug
A recent PR uses Py_SET_TYPE -- this was to solve another deprecated / changed API issue.
Unfortunately this was only first added in 3.9, so this broke compatibility with older versions

To Reproduce
Build using Python <= 3.8

Expected behavior
Should work with at least down to 3.6, preferably more.

System observed on:
N/A

Reporter Info
Joseph Hickey, Vantage Systems, Inc (based on other user report)