haskell-graphviz: disable test suite because it runs way too long

The test suite runs for ages, i.e. 1+ hours. That seems a little excessive.

pkgs/development/libraries/haskell/graphviz/default.nix

@@ -16,6 +16,7 @@ cabal.mkDerivation (self: {
   ];
   testDepends = [ fgl filepath QuickCheck systemGraphviz text ];
   jailbreak = true;
+  doCheck = false;
   meta = {
     homepage = "http://projects.haskell.org/graphviz/";
     description = "Bindings to Graphviz for graph visualisation";