Remove python 3.8 from tests

[cboulay]

No description provided.

[griffinmilsap]

Possible we should bump to minimum Python 3.10? Lots of typehinting conveniences there, and dataclasses with keyword-only arguments that could solve some QOL issues with messages today -- specifically dataclasses with init=true (or base-class dataclasses with init=true) but arguments with defaults being specified before arguments without defaults.

[cboulay]

I figured you'd be the one to want older Python support for certain devices that might be lagging behind. I only use ezmsg on relatively modern hardware so I'm fine with bumping the minimum version.

(init=true might break fast_replace)