flake.nix: Move vm out of nixosConfigurations so that checks work

flake.nix

@@ -77,10 +77,15 @@
       inherit (nixpkgs.legacyPackages.${system}) writeShellScript;
     in {
       default = let
-        vm = self.lib.makeNixosSystem {
-          inherit system;
-          extraModules = [(import ./configuration/hardware-specific/vm.nix)];
-        };
+        vm =
+          (self.lib.makeNixosSystem {
+            inherit system;
+            extraModules = [(import ./configuration/hardware-specific/vm.nix)];
+          })
+          .config
+          .system
+          .build
+          .vm;
 
         qemuNetOpts = self.lib.makeQemuNetOpts {
           "2222" = "2222";
@@ -93,7 +98,7 @@
         program = builtins.toString (writeShellScript "run-vm" ''
           export QEMU_OPTS="-m 3941 -smp 2 -display curses"
           export QEMU_NET_OPTS="${qemuNetOpts}"
-          "${vm.config.system.build.vm}/bin/run-tlaternet-vm"
+          "${vm}/bin/run-tlaternet-vm"
         '');
       };