message: Fix compilation error with clang 11
diff: @@ -516,9 +516,9 @@ namespace externalexecutor
  ccf::ClaimsDigest::Digest::SIZE,
  payload_digest.size()));
  }
  - claims.set(crypto::Sha256Hash::from_span(
  - {(uint8_t*)payload_digest.data(),
  - ccf::ClaimsDigest::Digest::SIZE}));
  + const std::span<const uint8_t, crypto::Sha256Hash::SIZE> digest_span{
  + (uint8_t*)payload_digest.data(), ccf::ClaimsDigest::Digest::SIZE};
  + claims.set(crypto::Sha256Hash::from_span(digest_span));
  }
  auto& active_request = it->second.submitted_requests.front();
  