Retry private Azure downloads with authentication (#21318)
Azure Storage can report an anonymous request to a private configured
endpoint as `409 PublicAccessNotPermitted`, so uv returned the response
without attempting configured credentials. Treat that exact error only
as an authentication failure for configured Azure endpoints, allowing
the normal credential discovery and signed retry path to run. For
example, a private `https://example.blob.core.windows.net/python/...`
download can retry with Azure credentials after the anonymous probe is
denied.
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Co-authored-by: Zanie Blue <contact@zanie.dev>