pypy3Packages.six: Disable test that loads native library

```
for c in ['5.3', '5.2', '5.1', '5.0', '4.9', '4.8', '4.7', '4.6', '4.5']:
    libpath = ctypes.util.find_library('db-%s' % c)
    if libpath:
        break
else:
    raise ModuleNotFoundError("Cannot find dbm library", name='_dbm')
    ModuleNotFoundError: Cannot find dbm find_library
```

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

@@ -1,6 +1,7 @@
 { lib
 , buildPythonPackage
 , fetchPypi
+, isPyPy
 , pytestCheckHook
 }:
 
@@ -19,6 +20,11 @@ buildPythonPackage rec {
     pytestCheckHook
   ];
 
+  pytestFlagsArray = if isPyPy then [
+    # uses ctypes to find native library
+    "--deselect=test_six.py::test_move_items"
+  ] else null;
+
   pythonImportsCheck = [ "six" ];
 
   meta = {