fix trivy scan parsing of cluster image file

Author: sjpb

.github/workflows/trivyscan.yml

@@ -72,7 +72,7 @@ jobs:
       - name: Parse image name json
         id: manifest
         run: |
-          IMAGE_NAME=$(jq --arg version "${{ matrix.build }}" -r '.cluster_image_names[$version]' "${{ env.JSON_PATH }}")
+          IMAGE_NAME=$(jq --arg version "${{ matrix.build }}" -r '.cluster_image_names[$version].default' "${{ env.JSON_PATH }}")
           echo "image-name=${IMAGE_NAME}" >> "$GITHUB_OUTPUT"
 
       - name: Download image