forge-alist: Add entry for ssh.github.com

As documented in
https://docs.github.com/en/authentication/troubleshooting-ssh/using-ssh-over-the-https-port.

Closes #708.

Author: tarsius

lisp/forge-core.el

@@ -59,6 +59,8 @@
   '(;; Forges
     ("github.com" "api.github.com"
      "github.com" forge-github-repository)
+    ("ssh.github.com" "api.github.com"
+     "github.com" forge-github-repository)
     ("gitlab.com" "gitlab.com/api/v4"
      "gitlab.com" forge-gitlab-repository)
     ("salsa.debian.org" "salsa.debian.org/api/v4"