Backport #17281
There is a subtle bug in the SSH library x/crypto/ssh which makes the incorrect
assumption that the public key type is the same as the signature algorithm type.
This means that only ssh-rsa signatures are offered by default.
This PR adds a workaround around this problem.
Fix#17175
Signed-off-by: Andrew Thornton <art27@cantab.net>
Co-authored-by: techknowlogick <techknowlogick@gitea.io>