use read lock to block out writer for greater code coverage

Author: tdyas

src/sync.rs

@@ -1408,7 +1408,7 @@ mod tests {
         std::thread::scope(|s| {
             s.spawn(|| {
                 Python::attach(|py| {
-                    let b = rwlock.write_py_attached(py).unwrap();
+                    let b = rwlock.read_py_attached(py).unwrap();
                     barrier.wait();
                     // sleep to ensure the other thread actually blocks
                     std::thread::sleep(std::time::Duration::from_millis(10));