Add REUSE compliance checker to CI

BUILD.gn

@@ -1,17 +1,7 @@
-# Copyright (C) 2018-2023 The ANGLE Project Authors.
-# Copyright (C) 2019-2023 LunarG, Inc.
+# Copyright 2018-2023 The ANGLE Project Authors.
+# Copyright 2019-2023 LunarG, Inc.
 #
-# Licensed under the Apache License, Version 2.0 (the "License");
-# you may not use this file except in compliance with the License.
-# You may obtain a copy of the License at
-#
-#     https://www.apache.org/licenses/LICENSE-2.0
-#
-# Unless required by applicable law or agreed to in writing, software
-# distributed under the License is distributed on an "AS IS" BASIS,
-# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-# See the License for the specific language governing permissions and
-# limitations under the License.
+# SPDX-License-Identifier: Apache-2.0
 
 import("//build_overrides/vulkan_headers.gni")