Fix compatibility with cythonized tasks. (#3246)

`types.GeneratorType` is not compatible with the generator type of
Cython. This leads to `_run_get_new_deps()` returning directly when
the task is from a cythonized module and [yields dynamic
dependencies](https://luigi.readthedocs.io/en/stable/tasks.html?highlight=yield#dynamic-dependencies).

luigi/worker.py

@@ -29,6 +29,7 @@
 """
 
 import collections
+import collections.abc
 import datetime
 import getpass
 import importlib
@@ -47,7 +48,6 @@
 import threading
 import time
 import traceback
-import types
 
 from luigi import notifications
 from luigi.event import Event
@@ -137,7 +137,7 @@ def __init__(self, task, worker_id, result_queue, status_reporter,
     def _run_get_new_deps(self):
         task_gen = self.task.run()
 
-        if not isinstance(task_gen, types.GeneratorType):
+        if not isinstance(task_gen, collections.abc.Generator):
             return None
 
         next_send = None