Don't hard-fail the distro validation script when a download fails

[Blue (OneBlue)]

Summary of the Pull Request

This change updates the distro validation script not to fail immediately if a download fails. This makes it easier to identify when multiple distros fail to download

PR Checklist

• Closes: Link to issue #xxx
• Communication: I've discussed this with core contributors already. If work hasn't been agreed, this work might be rejected
• Tests: Added/updated if needed and all pass
• Localization: All end user facing strings can be localized
• Dev docs: Added/updated if needed
• Documentation updated: If checked, please file a pull request on our docs repo and link it here: #xxx

Detailed Description of the Pull Request / Additional comments

Validation Steps Performed

[Copilot]

Pull request overview

This pull request updates the modern distribution validation script to continue validation when a downloaded .wsl payload can’t be parsed as a tar, so the script can report multiple failures in one run.

Changes:

• Wrap read_tar(...) for HTTP(S) downloads in a try/except to avoid aborting the whole script on tar read failures.
• Emit an error(...) entry when tar parsing fails instead of letting the exception unwind.