What version of Hugo are you using (hugo version)?

$ hugo version
hugo v0.139.4+extended linux/amd64 BuildDate=unknown

Does this issue reproduce with the latest release?

Yes, it does.

When using the string:

# more publishable markdown files...

in a yaml-codeblock, like this

      - name: Copy over new files
        run: |
            # Whitelist of all publishable wiki articles
            cp index.md $content
            # more publishable markdown files...

instead of the block an e> gets generated. When removing the comment, everything works fine. I also tried different strings with which, it sometimes worked and sometimes not. I cannot guess pattern, when the error occurs.

Also there is no special output when building the site. I guess there is something wrong with goldmark but I do not fully understand how hugo uses goldmark. So I'm approaching you guys at first.

Thanks for your time. I would be happy to provide more information on this issue.