`Sync::RWLock#test_lock_write_waits_for_all_read_locks_to_be_unlocked` test regularly fails on macOS

ysbaddaden

This happens on both Intel and ARM so it's not an ARM issue (like atomic memory ordering), so maybe another case of "a thread assumption that's wrong on darwin"? See for example https://github.com/ysbaddaden/sync/actions/runs/18980770977/job/54212434592