pypy3Packages.yapf: Disable tests

Cannot be tested, because it is using nose for tests, which is broken
for pypy.

pkgs/development/python-modules/yapf/default.nix

@@ -1,6 +1,7 @@
 { lib
 , buildPythonPackage
 , fetchPypi
+, isPyPy
 , nose
 }:
 
@@ -13,6 +14,9 @@ buildPythonPackage rec {
     hash = "sha256-o/UIXTfvfj4ATEup+bPkDFT/GQHNER8FFFrjE6fGfRs=";
   };
 
+  # nose is unavailable on pypy
+  doCheck = !isPyPy;
+
   nativeCheckInputs = [
     nose
   ];