TARGET_HEADS_FILE 미정의로 터지던(LLM의표현) 부분을 제거

.gitea/workflows/backup.yml

@@ -333,7 +333,6 @@ jobs:
             fi
             heads_detail="src=${source_commit} tgt=${target_commit:-none}"
             exists_text=$(${repo_exists} && echo "true" || echo "false")
-            echo -e "${repo_name}\tmain\t${target_commit:-}\t${exists_text}" >> "${TARGET_HEADS_FILE}"
 
             decision=""
             if ! ${repo_exists}; then