Decrease collector block size so a block fits into exactly four 64-by…

…tes-long cache lines.

src/gil.rs

@@ -284,7 +284,7 @@ struct PendingDecRef(NonNull<ffi::PyObject>);
 unsafe impl Send for PendingDecRef {}
 
 #[cfg(not(pyo3_disable_reference_pool))]
-static POOL: Collector<PendingDecRef, 32> = Collector::new();
+static POOL: Collector<PendingDecRef, 30> = Collector::new();
 
 fn update_counts(_py: Python<'_>) {
     for obj in POOL.collect() {