Fix malloc/new mismatch in api_fuzzer (#27531)

test/core/end2end/fuzzers/api_fuzzer.cc

@@ -383,7 +383,7 @@ grpc_ares_request* my_dns_lookup_ares_locked(
     std::unique_ptr<grpc_core::ServerAddressList>* /*balancer_addresses*/,
     char** /*service_config_json*/, int /*query_timeout*/,
     std::shared_ptr<grpc_core::WorkSerializer> /*combiner*/) {
-  addr_req* r = static_cast<addr_req*>(gpr_malloc(sizeof(*r)));
+  addr_req* r = new addr_req();
   r->addr = gpr_strdup(addr);
   r->on_done = on_done;
   r->addrs = nullptr;