message: Wrap {absl,crypto::tink::util}::Status::message() calls in std::string() when called in protobuf setters in tink/testing/.
diff: @@ -377,20 +377,20 @@ grpc::Status JwtImpl::PublicKeyVerifyAndDecode(grpc::ServerContext* context,
  StatusOr<std::unique_ptr<KeysetHandle>> keyset_handle =
  JwkSetToPublicKeysetHandle(request->jwk_set());
  if (!keyset_handle.ok()) {
  - response->set_err(keyset_handle.status().message());
  + response->set_err(std::string(keyset_handle.status().message()));
  return ::grpc::Status::OK;
  }
  std::stringbuf keyset;
  StatusOr<std::unique_ptr<crypto::tink::BinaryKeysetWriter>> writer =
  BinaryKeysetWriter::New(absl::make_unique<std::ostream>(&keyset));
  if (!writer.ok()) {
  - response->set_err(writer.status().message());
  + response->set_err(std::string(writer.status().message()));
  return ::grpc::Status::OK;
  }
  crypto::tink::util::Status status =
  CleartextKeysetHandle::Write(writer->get(), **keyset_handle);
  if (!status.ok()) {
  - response->set_err(status.message());
  + response->set_err(std::string(status.message()));
  return ::grpc::Status::OK;
  }
  response->set_keyset(keyset.str());
  