Update debian11_container.sh

ct/debian11_container.sh

@@ -15,6 +15,7 @@ set -o nounset
 set -o pipefail
 shopt -s expand_aliases
 alias die='EXIT=$? LINE=$LINENO error_exit'
+CHECKMARK='\033[0;32m\xE2\x9C\x94\033[0m'
 trap die ERR
 trap cleanup EXIT