Potential fix for code scanning alert no. 385: Workflow does not contain permissions

Signed-off-by: ZePan110 <ze.pan@intel.com>

Co-authored-by: Copilot Autofix powered by AI <62310815+github-advanced-security[bot]@users.noreply.github.com>

Author: ZePan110

.github/workflows/pr-image-size.yml

@@ -1,6 +1,8 @@
 # Copyright (C) 2024 Intel Corporation
 # SPDX-License-Identifier: Apache-2.0
 name: Check Docker Image Size Change
+permissions:
+  contents: read
 
 on:
   pull_request: