-fixed shellcheck issue

src/usr/local/bin/validate_workflow.sh

@@ -345,7 +345,7 @@ get_cli_args() {
             exit 1
         fi
         if [[ ! -f "${FILE_NAME}" ]]; then
-          error "filename '$FILE_NAME' for param --single-file does not exist!"
+          error "filename '${FILE_NAME}' for param --single-file does not exist!"
           exit 1
         fi
       else