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
```

Start by reproducing tests::test_waker_threaded on macOS with Rust 1.70 and inspect the failure at src/lib.rs:1003:48. Compare the failing unwrap_err result with the test's expected behavior, and consider the work done when the test no longer fails or hangs in that environment.

Written by the indexing model from the issue text.