treewide: switch to nativeCheckInputs

checkInputs used to be added to nativeBuildInputs. Now we have
nativeCheckInputs to do that instead. Doing this treewide change allows
to keep hashes identical to before the introduction of
nativeCheckInputs.

pkgs/development/python2-modules/pip/default.nix

@@ -28,7 +28,7 @@ buildPythonPackage rec {
   # to force it a little.
   pipInstallFlags = [ "--ignore-installed" ];
 
-  checkInputs = [ mock scripttest virtualenv pretend pytest ];
+  nativeCheckInputs = [ mock scripttest virtualenv pretend pytest ];
   # Pip wants pytest, but tests are not distributed
   doCheck = false;