tests.cuda.cuda-sample_*: Init at supported CUDA toolkit versions

Since CUDA is unfree, we won't actually use this when testing Nixpkgs
officially. But I want to include this as they are useful for users of
Nixpkgs trying to set up / debug a CUDA environment.

pkgs/test/default.nix

@@ -47,5 +47,7 @@ with pkgs;
 
   texlive = callPackage ./texlive {};
 
+  cuda = callPackage ./cuda { };
+
   writers = callPackage ../build-support/writers/test.nix {};
 }