When a donor tries to use a card that Adyen can't find an acquirer for, we show them an error message and also send a failmail.
The donor-facing error should be enough. Stop sending the failmail.
This has happened most frequently trying to accept EUR donations in European countries via UATP cards and Korean local cards.
We should probably add another error code to the SmashPig error enum and map Adyen error 905_1 to that.