nixos/tests/wine: fix gecko check and diskSize type

nixos/tests/wine.nix

@@ -3,7 +3,7 @@
 }:
 
 let
-  inherit (pkgs.lib) concatMapStrings listToAttrs;
+  inherit (pkgs.lib) concatMapStrings listToAttrs optionals optionalString;
   inherit (import ../lib/testing-python.nix { inherit system pkgs; }) makeTest;
 
   hello32 = "${pkgs.pkgsCross.mingw32.hello}/bin/hello.exe";
@@ -17,7 +17,7 @@ let
 
       machine = { pkgs, ... }: {
         environment.systemPackages = [ pkgs."${packageSet}"."${variant}" ];
-        virtualisation.diskSize = "800";
+        virtualisation.diskSize = 800;
       };
 
       testScript = ''
@@ -27,6 +27,9 @@ let
               "bash -c 'wine ${exe} 2> >(tee wine-stderr >&2)'"
           )
           assert 'Hello, world!' in greeting
+        ''
+        # only the full version contains Gecko, but the error is not printed reliably in other variants
+        + optionalString (variant == "full") ''
           machine.fail(
               "fgrep 'Could not find Wine Gecko. HTML rendering will be disabled.' wine-stderr"
           )
@@ -37,5 +40,9 @@ let
 
   variants = [ "base" "full" "minimal" "staging" "unstable" ];
 
-in listToAttrs (map (makeWineTest "winePackages" [ hello32 ]) variants
-  ++ map (makeWineTest "wineWowPackages" [ hello32 hello64 ]) variants)
+in
+listToAttrs (
+  map (makeWineTest "winePackages" [ hello32 ]) variants
+  ++ optionals pkgs.stdenv.is64bit
+    (map (makeWineTest "wineWowPackages" [ hello32 hello64 ]) variants)
+)