Update libgit2 to fix misalignment issue on arm64 (#646)

Also update git_cert_ssh_t to include lost value

Author: Alovchin91

libgit2-sys/lib.rs

@@ -473,6 +473,7 @@ git_enum! {
         GIT_CERT_SSH_MD5 = 1 << 0,
         GIT_CERT_SSH_SHA1 = 1 << 1,
         GIT_CERT_SSH_SHA256 = 1 << 2,
+        GIT_CERT_SSH_RAW = 1 << 3,
     }
 }