Ignore flaky VirusTotal docs link

[MikeMcQuaid]

• www.virustotal.com sometimes returns 503 during HTMLProofer external link checks.
• Keeping it in ignore_urls avoids unrelated docs CI failures.

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[Copilot]

Pull request overview

This PR updates the documentation site’s HTMLProofer configuration to avoid flaky CI failures caused by intermittent 503 responses from VirusTotal during external link checking.

Changes:

• Add https://www.virustotal.com to ignore_urls in the docs HTMLProofer check configuration.

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