fails to test examples without feature std

[jonassmedegaard]

The command cargo test --all-targets --no-default-features fails like this:

514s error[E0425]: cannot find function `spawn_local` in crate `async_task`
514s   --> examples/spawn-local.rs:22:40
514s    |
514s 22 |     let (runnable, task) = async_task::spawn_local(future, schedule);
514s    |                                        ^^^^^^^^^^^ not found in `async_task`
514s 
514s For more information about this error, try `rustc --explain E0425`.
514s error: could not compile `async-task` due to previous error