Fix issue with markdown linter github action in file docs-lint.yml

Currently supermarket markdown linter github action is not highlighting the lint issues with any markdown file. It's passing the check even if the .md files have lint issus. Need to fix this.

Occurred for this PR: https://github.com/chef/supermarket/pull/2216/files
file: docs-chef-io/content/supermarket/supermarket_upgrade.md