centipede::BlobSequence uses deprecated is_pod

[nico]

https://github.com/google/fuzztest/blob/main/centipede/shared_memory_blob_sequence.h#L72

  // Writes `tag`/`value` as a blob. `T` should be a POD.
  // Returns true on success.
  template <typename T>
  bool Write(Blob::SizeAndTagT tag, T value) {
    static_assert(std::is_pod_v<T>, "T must be a POD");
    return Write(
        {tag, sizeof(value), reinterpret_cast<const uint8_t *>(&value)});
  }

is_pod is deprecated in C++20 and was marked as such in libc++ in llvm/llvm-project#129471

This probably wants to use std::is_standard_layout instead.

[nico]

@lszekeres per https://issues.chromium.org/issues/402772406#comment11 :)