Docs build fails due to usage of imp module

https://app.readthedocs.org/projects/adafruit-circuitpython-apds9960/builds/26874191/

```
  File "/home/docs/checkouts/readthedocs.org/user_builds/adafruit-circuitpython-apds9960/checkouts/stable/docs/conf.py", line 26, in <module>
    import imp
ModuleNotFoundError: No module named 'imp'
```

This was removed in 3.12 after being deprecated for a while. We'll need to migrate to importlib