Cannot provide PIN for second plugged-in key

[str4d]

What were you trying to do

I had two YubiKeys plugged in, and an age file encrypted to both of them. However, the first YK it selected I didn't know the PIN for, so I clicked "Cancel" hoping it would skip to the next key.

What happened

Error: '⁨age-plugin-yubikey⁩' couldn't use an identity: ⁨A PIN is required for YubiKey with serial ######

[str4d]

#63 enables YubiKeys to be skipped when we ask them to be plugged in, but we still want to handle this case (plugged in, but can't use the PIN). @FiloSottile is of the opinion that if an error occurs during PIN requesting for unwrapping, we should just automatically skip, without returning an explicit error across the plugin protocol (which can cause an abort).