ssh: Support newer host key signatures

[andrm]

Right now I only get
debug2: host key algorithms: ssh-rsa,ssh-dss
from gitblit SSHD.
Fedora 33 has changed, it will not accept ssh-rsa (from the server) anymore:
debug1: Offering public key: /home/XXXX/.ssh/id_rsa RSA SHA256:XXXXXXXXXXXXXX agent
debug1: send_pubkey_test: no mutual signature algorithm

Workaround: Set this in .ssh/config:
Host HOSTNAME
PubkeyAcceptedKeyTypes +ssh-rsa

I think SSHD is capable of newer host key sigs

[flaix]

Thank you for reporting it and including a workaround.
Support will be included when PR #1272 is merged. But I guess we need to make sure that the initial server keys get generated with the new chipers, too, so this issue is left as the reminder to implement that.

[bturner]

This just came up on the public Git mailing list. Public key authentication fails because the user is on OpenSSH 8.8, which disables ssh-rsa by default. (Fedora jumped on this early, but it's starting to hit more Linux distributions now.)