Calling run() after crashing a host errors

[mcches]

Repro:

#[test]
fn run_after_host_crashes() -> Result {
    let mut sim = Builder::new().build();

    sim.host("h", || async { future::pending().await });

    sim.crash("h");

    sim.run()
}

Fails with:

running 1 test
Error: JoinError::Cancelled(Id(1))
test sim::test::run_after_host_crashes ... FAILED

failures:

failures:
    sim::test::run_after_host_crashes

test result: FAILED. 0 passed; 1 failed; 0 ignored; 0 measured; 10 filtered out; finished in 0.00s