Fixes git clone tests when running against OpenSSH v8.8
OpenSSH 8.8 turns off the hostkey algorithm 'ssh-rsa' by default. See: https://www.openssh.com/txt/release-8.8
Unfortunately, libssh2 (and therefore libgit2) do not yet support the newer sha2-based ssh hostkey algorithms. See upstream issue: https://github.com/libssh2/libssh2/issues/536
This explicitly re-enables ssh-rsa on the sshd that is spun up for testing to ensure that libgit2 can handshake with it again.