deploy: Only send the wanted machine configuration

This avoids having secrets that are managed with git-crypt on every
system.

deploy.nix

@@ -34,6 +34,14 @@ let
                 type = "exclude";
                 pattern = "*.qcow2";
               }
+              {
+                type = "include";
+                pattern = "/machines/${hostname}/";
+              }
+              {
+                type = "exclude";
+                pattern = "/machines/*/";
+              }
             ];
           };
           nixos-config.symlink = "config/machines/${hostname}/configuration.nix";