nixos/forgejo: pass {env}GIT_PROTOCOL via ssh to forgejo

when using the host's openssh service (not the builtin golang one).

This enables the use of the much faster and more efficient wire protocol
version 2.
See https://git-scm.com/docs/protocol-v2

nixos/modules/services/misc/forgejo.nix

@@ -632,6 +632,8 @@ in
       };
     };
 
+    services.openssh.settings.AcceptEnv = mkIf (!cfg.settings.START_SSH_SERVER or false) "GIT_PROTOCOL";
+
     users.users = mkIf (cfg.user == "forgejo") {
       forgejo = {
         home = cfg.stateDir;