fix: fix Django ASGI integration on Python 3.12

[bellini666]

Upgrading a Django ASGI application to Python 3.12 broke because of the integration not being able to identify that the middleware being called was async.

This is due to Python 3.12 replacing setting _is_coroutine = asyncio.coroutines._is_coroutine with inspect.markcoroutinefunction

This ports the fix from asgiref to make sure sentry_sdk can support multiple python versions.

I thought about importing it from asgiref, but not sure how the maintainers feel about requiring it as a dependency (although it is already a django's dependency)

[sentrivana]

Hey @bellini666, thanks a lot for the fix! Taking a look.

[sentrivana]

LGTM. I also think porting the asgiref shim is a good way to go about this, even if asgiref is a Django dependency.

Thanks again for the fix, will merge this now.