Making sure SecretKey is zeroized on drop

I was trying to make my newtype of SecretKey zeroize properly, and realized I can't even trigger zeroization for SecretKey itself. Consider the code:

use k256::SecretKey;
use rand_core::OsRng;

fn main() {
    let sk = SecretKey::random(&mut OsRng);

    let ptr = &sk as *const SecretKey;
    let ptr_u8 = ptr as *const u8;

    println!("Pointer: {:p}", ptr);

    drop(sk);

    println!("Memory: {:?}", unsafe {
        core::slice::from_raw_parts(ptr_u8, 4)
    });
}

k256 has zeroize feature enabled in Cargo.toml. This still gives a non-zero output after SecretKey was dropped, despite there being a Drop implementation in secret_key.rs that calls zeroize(). Am I misunderstanding something?

Start by reproducing the supplied example with the zeroize feature enabled, then inspect the Drop implementation in secret_key.rs and the feature configuration in Cargo.toml. Determine whether the observed memory contents match the intended zeroization behavior and document or correct the behavior, with a focused regression test if the repository’s existing tests provide a suitable location.