chore: fix cache flush template (#4809)

Signed-off-by: Neal Vaidya <nealv@nvidia.com>

.github/workflows/templates/akamai-eccu-flush.xslt

-<?xml version="1.0" encoding="UTF-8"?>
+<?xml-stylesheet type="text/xsl" href="akamai-eccu-flush.xslt"?>
+<!--
+Copyright (c) 2025, NVIDIA CORPORATION. All rights reserved.
+
+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.
+-->
 <!--
   Akamai ECCU (Edge Content Control Utility) XML Generator