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Code improvement description

When PyPI.org is down, Dependabot Core returns the update job as failed with a private_source_authentication_failure error.

This means we categorize the issue as a 'non viable update' thinking it is a user-configuration problem when in fact it is a service issue that should trip alarms.

We should take the dependency source into consideration for pip specifically and check if there is a way we can do generically for package managers that don't throw a specific error for their community index being down.