test_waker_threaded fails or hangs in Rust 1.70

Running `test_waker_threaded` in Rust 1.70 on macOS almost always either fails or hangs indefinitely.

```
---- tests::test_waker_threaded stdout ----
thread 'tests::test_waker_threaded' panicked at 'called `Result::unwrap_err()` on an `Ok` value: ()', src/lib.rs:1003:48
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace
```