Sym Alg Support (AEADED) tests (v5) do not properly check used sym alg

When checking symmetric algorithm support for v5 keys using AEADED packets, the test suite behaves inconsistently.

Especially when testing, if the producer uses invalid symmetric algorithms (IDEA, etc.) that cannot be used with AEADED packets, on one hand the suite rewards implementations for falling back to SEIPDv1, even though the test keys do no advertise support, while at the same time punishing implementations that do use AEADED, but fall back to a valid, yet not advertised symmetric key algorithm (AES128 in my case).

I assume, this is due to Sequoia not supporting AEADED packets and taking a shortcut here. A better solution would probably be to check the packet type AND the emitted session key, similar to how the check is done with v6 artifacts.