update minimum python version to 3.9

[FoamyGuy]

cc @makermelissa we discussed minimum version for Blinka and Circuitpython_Typing in the weeds during Monday's meeting a bit. Am definitely open to input from you as well on updating it, and if you know whether there is anywhere else in this repo that it might need to be changed.

[makermelissa]

One of the things holding us back on updating to a more recent version of python is the Jetson Nano, which last time I checked would only install up to version 3.8. So before we merge this I need to check a few things:

1. Update the Jetson Nano and see if Python > 3.8 is available (internet is currently down, so will need to wait until tomorrow unless I figure out an alternative sooner)
2. If not, there may be an alternate way such as building from sources, so a guide section update would need to be done in such a case.

[makermelissa]

Ok, I figured out a good alternative and will give it a shot.

[makermelissa]

Python 3.8 is still the latest through sudo apt install. There may be another way to update and I'll look into that.