Drop support for Python 3.7 and test with 3.12

[edgarrmondragon]

• 3.7 EOL was 27 Jun 2023
• 3.12 was released on 02 Oct 2023

[edgarrmondragon]

Data to back up dropping 3.7:

It has consistently been <1% for many months now.

(Data is from https://pypistats.org, but I find their line charts harder to read 😅 )