nixos/test-driver: fix duplicate names in type check

ignore the NixOS configuration's hostname and only use the test driver
attribute for the type hints. This allows for setting a different host
name than the node name in the test without trigggering type errors in
the typecheck phase.

co-authored-by: phanirithvij <phanirithvij2000@gmail.com>

nixos/lib/testing/driver.nix

@@ -36,7 +36,7 @@ let
       theOnlyMachine =
         let
           exactlyOneMachine = lib.length (lib.attrValues config.nodes) == 1;
-          allMachineNames = map (c: c.system.name) (lib.attrValues config.allMachines);
+          allMachineNames = lib.attrNames config.allMachines;
         in
         lib.optional (exactlyOneMachine && !lib.elem "machine" allMachineNames) "machine";