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

Changed files
+2
nixos
modules
services
+2
nixos/modules/services/misc/forgejo.nix
···
};
};
+
services.openssh.settings.AcceptEnv = mkIf (!cfg.settings.START_SSH_SERVER or false) "GIT_PROTOCOL";
+
users.users = mkIf (cfg.user == "forgejo") {
forgejo = {
home = cfg.stateDir;