[memory_usage] Use a named target for the client (#33258)

Allows usage on machines that don't support ipv4.

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test/core/memory_usage/memory_usage_test.cc

@@ -95,7 +95,7 @@ int RunCallBenchmark(char* root, std::vector<std::string> server_scenario_flags,
       absl::StrCat(root, "/memory_usage_client",
                    gpr_subprocess_binary_extension()),
       "--target",
-      grpc_core::JoinHostPort("127.0.0.1", port),
+      grpc_core::JoinHostPort("localhost", port),
       "--grpc_experiments",
       std::string(grpc_core::ConfigVars::Get().Experiments()),
       absl::StrCat("--warmup=", 10000),
@@ -135,7 +135,7 @@ int RunChannelBenchmark(char* root) {
       absl::StrCat(root, "/memory_usage_callback_client",
                    gpr_subprocess_binary_extension()),
       "--target",
-      grpc_core::JoinHostPort("127.0.0.1", port),
+      grpc_core::JoinHostPort("localhost", port),
       "--nosecure",
       absl::StrCat("--server_pid=", svr.GetPID()),
       absl::StrCat("--size=", absl::GetFlag(FLAGS_size))};