Mute ShellCheck warning about temp var

src/include-sh/mdfmt.sh

@@ -78,6 +78,7 @@ _mdfmt__indent() {
     test "$Elem" == h2 && { cat; return; }
     test "$Elem" == h3 && { cat; return; }
     pfx=$(
+        #shellcheck disable=SC2034
         for n in $(seq 1 "$Nest"); do
             printf '    '
         done