[llvm] [python] Bump Python minimum version to 3.8 (PR #78828)

[Aiden Grossman via llvm-commits]

boomanaiden154 wrote:

Alright. I'm going to merge this tonight (@linux4life798 you should probably apply for commit access soonish too now that you've landed a couple commits) in the evening when buildbot traffic is hopefully low. I'll keep an eye on the post-commit bots and see what ends up failing. I'd almost expect failures, so wouldn't be surprised if it gets reverted initially, but that will let us know what breaks and we can move from there.

https://github.com/llvm/llvm-project/pull/78828