github actions: experiment with workflow error commands

.github/workflow-scripts/check-gofmt.sh

@@ -6,6 +6,10 @@ fmt_list="$(gofmt -l "$@")"
 
 if [ -n "$fmt_list" ]; then
   echo "Check gofmt failed: " >&2
-  echo "${fmt_list}" | sed -e 's/^/\t/' >&2
+
+  for file in "$fmt_list"; do
+    echo "::error file=${file},title=gofmt::gofmt check failed"
+    echo "\t$file" >&2
+  done
   exit 1
 fi