* Update metadata-syntax-for-github-actions.md
I tried to use another name than Dockerfile, the build fails saying:
`docker: invalid reference format: repository name must be lowercase.`
* Update content/actions/creating-actions/metadata-syntax-for-github-actions.md
Thanks, I struggled to find the correct words and not change the text too much
Co-authored-by: hubwriter <hubwriter@github.com>
Co-authored-by: hubwriter <hubwriter@github.com>