Virtualbox: Fix type error in `networking.interfaces.vboxnet0.ipv4.addresses`

This error introduced in e239c1e5820bdbb3d94ccc46e2d6756b0d37057d
prevented evaluation on my machine.

nixos/modules/virtualisation/virtualbox-host.nix

···
           '';
       };
 
-    networking.interfaces.vboxnet0.ipv4.addresses = { address = "192.168.56.1"; prefixLength = 24; };
+    networking.interfaces.vboxnet0.ipv4.addresses = [{ address = "192.168.56.1"; prefixLength = 24; }];
     # Make sure NetworkManager won't assume this interface being up
     # means we have internet access.
     networking.networkmanager.unmanaged = ["vboxnet0"];