chore: drop long-unsupported Python 3.7

[mgrdcm]

Python 3.7 hasn't been supported in ages, and it's causing errors on CI actions so let's just drop it.

It appears that dropping Python 3.7 is desired anyway!

[crccheck]

Thanks, I'll need to dig around a bit to make sure, and release this as a major version as a way to signal something got dropped. I may look into dropping some other old versions too if they're also very old

[mgrdcm]

Thanks, I'll need to dig around a bit to make sure, and release this as a major version as a way to signal something got dropped. I may look into dropping some other old versions too if they're also very old

That makes sense - would you like me to update this to get rid of other older versions as well? I'd recommend dropping Python older than 3.9 (3.8 and before are EOL) and older than 4.2 (4.1 and before are EOL). Then all that could go into one breaking/major version update.