In 93c8007, SRP signature errors were made non-fatal because many
users got the following error:
openpgp: unsupported feature: public key algorithm 22
This is because Protonmail started signing these messages with an
EDDSA key, an algorithm which the Go OpenPGP library does not
support. The switch to github.com/protonmail/crypto introduces this
algorithm, so messages that haven't been tampered with should pass
the verification.
Temporarily make signature errors non-fatal because the Go OpenPGP library is
missing some features we need:
openpgp: unsupported feature: public key algorithm 22
This doesn't really weaken our security since we weren't checking the signature
key anyway. To completely fix this issue, we need to upstream the required
key algorithm.
Fixes https://github.com/emersion/hydroxide/issues/46