Fix Nanny subclass check

dask_cuda/local_cuda_cluster.py

@@ -340,7 +340,7 @@ def __init__(
                 "`distributed.local_cuda_cluster.LoggedWorker`, and specify "
                 "`log_spilling=False`."
             )
-        if not isinstance(worker_class, Nanny):
+        if not issubclass(worker_class, Nanny):
             worker_class = partial(Nanny, worker_class=worker_class)
 
         self.pre_import = pre_import