ci(kokoro): install addlicense tool on pre-commit presubmits

Co-authored-by: Wei Sun (Jack) <weisun@google.com>
PiperOrigin-RevId: 932061051

Author: Jacksunwei

contributing/samples/mcp/mcp_sse_mtls_agent/generate_mtls_certs.sh

@@ -1,4 +1,18 @@
 #!/bin/bash
+# Copyright 2026 Google LLC
+#
+# 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
+#
+#     http://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.
+
 set -e
 
 # Directory where this script is located