MutBumpVec crashes when bump pointer is not aligned

[bluurryy]

This will crash:

#[test]
fn unaligned_mut_bump_vec() {
    let mut bump: Bump = Bump::new();

    bump.alloc(8u8);

    let mut vec = MutBumpVec::new_in(&mut bump);
    vec.push(32u32);

    let slice = vec.into_slice();
    dbg!(slice);
}

[bluurryy]

This is because of a wrong debug assertion.