A DNSSEC validation can fail in the case where multiple DNSKEY are
available for a zone and none of them are supported, but for different
reasons: one has a DS record in the parent zone using an unsupported
digest while the other one uses an unsupported encryption algorithm.
Add a specific test case covering this flow and making sure that two
extended DNS error are provided: code 1 and 2, each of them highlighting
unsupported algorithm and digest.
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