Support redis-py 8.x

[amureki]

Hey there 👋

There was a recent redis-py release 8.0.0.

dramatiq[redis] currently requires redis>=4.0,<8.0, which prevents installing a new redis-py version.

Could we test compatibility with redis-py 8.x and, if compatible, relax the constraint to redis>=4.0,<9.0?
I am happy to provide a PR to see how the existing test suite reacts, but I'm not sure if I won't be missing any potential hidden quirks.

[amureki]

I submited #863 to see the regressions.