Github actions fails to parse single-letter subdomains (and single-letter domains, but that’s probably a much less common problem).
When you write a URL to standard out/err in a GitHub actions task, the UI parses it as a URL and makes the link clickable.
However, if the URL has a single letter subdomain, the parsing fails.
Here is an example run showing the problem. Open URL test and you’ll see that
https://a.example.com fails to parse, along with
a.co, but the URLs without single letter domains parse fine:
Single-letter subdomains are totally valid and should be parsed correctly. I created one for the express purpose of shortening URLs printed in GitHub actions, so this behavior bit me recently.