python3Packages.diskcache: disable test with django 4.1 issue

Signed-off-by: Florian Brandes <[e-mail]>

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

···
     "test_incr_version"
     "test_get_or_set"
     "test_get_many"
+    # see https://github.com/grantjenks/python-diskcache/issues/260
+    "test_cache_write_unpicklable_object"
   ];
 
   pythonImportsCheck = [