fix build error on AVX-512

[AquaEBM]

fixes the following compile error (on latest nightly):

error[E0658]: use of unstable library feature 'stdarch_x86_avx512'
  --> crates\core_simd\src\swizzle_dyn.rs:59:32
   |
59 |                 32 => transize(x86::_mm256_permutexvar_epi8, zeroing_idxs(idxs), self),
   |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: see issue #111137 <https://github.com/rust-lang/rust/issues/111137> for more information
   = help: add `#![feature(stdarch_x86_avx512)]` to the crate attributes to enable
   = note: this compiler was built on 2024-02-22; consider upgrading it if it is out of date

[calebzulawski]

Thanks!