Enhancement Suggestion: Use GitHub Actions Warning for Coveralls Binary Download Failures

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Background

This issue continues the discussion from #253 (fail-on-error doesn't work well when download fails), which addressed problems with the fail-on-error flag when the Coveralls binary download fails during GitHub Actions runs. While the main bug has been fixed, the user provided additional feedback and a suggestion to improve overall developer experience.

User's Suggestion

I'm not sure how easy it will be for me to spot this.

Some thoughts (in retrospect):

1. It'd be nice if it used a warning like:

   echo ::warning title=Coveralls::Failed to retrieve coveralls binary.
   

   As that'd surface the error on the summary page replacing
   as seen in https://github.com/PowerDNS/pdns/actions/runs/19316037365/attempts/1

Enhancement Request

When the Coveralls binary or its checksum fails to download in a workflow run (especially when fail-on-error: false), the action should emit a GitHub Actions warning using the ::warning workflow command. This would make such failures more visible in the GitHub Actions summary, rather than being hidden in log output.

Expected Behavior

• If the download fails and the action does not abort (because fail-on-error: false):
  • Print a warning with a descriptive title and message so it is easily visible on the workflow's summary page.

Example

echo "::warning title=Coveralls::Failed to retrieve coveralls binary."

Additional Context

• Original issue that prompted this enhancement: #253
• Example of how the problem is currently shown in the logs (as an error buried in lengthy output):
  
• Relevant workflow run: GitHub Actions Run Example

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This enhancement would improve usability by making intermittent or non-fatal Coveralls download issues much easier to notice and debug.

(If more details from the original issue are needed, please see #253 for full context.)