Merge pull request #264608 from nikstur/nix-channel-fix-default

nixos/nix-channel: fix subscribing to default channel

nixos/modules/config/nix-channel.nix

···
 
     systemd.tmpfiles.rules = lib.mkIf cfg.channel.enable [
       "f /root/.nix-channels -"
-      ''w "/root/.nix-channels" - - - - "${config.system.defaultChannel} nixos\n"''
+      ''w+ "/root/.nix-channels" - - - - ${config.system.defaultChannel} nixos\n''
     ];
   };
 }

nixos/tests/activation/nix-channel.nix

···
     nix.channel.enable = true;
   };
 
-  testScript = ''
-    print(machine.succeed("cat /root/.nix-channels"))
+  testScript = { nodes, ... }: ''
+    assert machine.succeed("cat /root/.nix-channels") == "${nodes.machine.system.defaultChannel} nixos\n"
   '';
+
 }