Fix BuildManifestBuilder.append_artifact to safely initialize artifact lists#5525

aravindkesavan wants to merge 1 commit intoopensearch-project:mainopensearch-project/opensearch-build:mainfrom

aravindkesavan:fix-artifacts-list-initializationaravindkesavan/opensearch-build:fix-artifacts-list-initializationCopy head branch name to clipboard