fix(conn/auto): hang on graceful shutdown when reading version

[dswij]

fixes hyperium/hyper#3576

This PR fixes graceful shutdown hanging when it's in the ReadVersion state due to open IOs.

For example, now in cargo run -p example-graceful-shutdown with nc

TRACE axum::serve: connection 127.0.0.1:52671 accepted
^C
TRACE axum::serve: received graceful shutdown signal. Telling tasks to shutdown
TRACE axum::serve: signal received in task, starting graceful shutdown
TRACE axum::serve: signal received, not accepting new connections
TRACE axum::serve: failed to serve connection: Cancelled ## < now shows as cancelled instead
TRACE axum::serve: connection 127.0.0.1:52671 closed
TRACE axum::serve: waiting for 0 task(s) to finish