fix(tests): fix malformed SPDX block comment in internal/main.cu

The SPDX header used bare `/* text` lines without closing `*/` on each
line, leaving an unclosed C comment. Subsequent `/*` markers triggered
-Werror=comment when internal/main.cu was compiled into new targets
(e.g. ROUTING_UNIT_TEST). Use the standard block-comment style matching
the rest of the test suite.

Signed-off-by: Ramakrishna Prabhu <ramakrishnap@nvidia.com>

Author: ramakrishnap-nv

cpp/tests/internal/main.cu

@@ -1,6 +1,8 @@
 /* clang-format off */
-/* SPDX-FileCopyrightText: Copyright (c) 2026, NVIDIA CORPORATION & AFFILIATES. All rights reserved.
-/* SPDX-License-Identifier: Apache-2.0
+/*
+ * SPDX-FileCopyrightText: Copyright (c) 2026, NVIDIA CORPORATION & AFFILIATES. All rights reserved.
+ * SPDX-License-Identifier: Apache-2.0
+ */
 /* clang-format on */
 
 #include <utilities/base_fixture.hpp>