fix: use correct type + use proper close method

[sicoyle]

I believe this should fix:

		== APP == Get response from hello_world_wf after terminate call: Terminated
		== APP == Get response from child_wf after terminate call: Terminated
		== APP == Instance Successfully Purged
		== APP == Traceback (most recent call last):
		== APP ==   File "/home/runner/work/python-sdk/python-sdk/examples/demo_workflow/app.py", line 220, in <module>
		== APP ==     main()
		== APP ==   File "/home/runner/work/python-sdk/python-sdk/examples/demo_workflow/app.py", line 216, in main
		== APP ==     workflow_runtime.shutdown()
		== APP ==   File "/home/runner/work/python-sdk/python-sdk/ext/dapr-ext-workflow/dapr/ext/workflow/workflow_runtime.py", line 269, in shutdown
		== APP ==     self.__worker.stop()
		== APP ==   File "/home/runner/work/python-sdk/python-sdk/.tox/examples/lib/python3.10/site-packages/durabletask/worker.py", line 743, in stop
		== APP ==     self._response_stream.cancel()
		== APP == AttributeError: 'generator' object has no attribute 'cancel'
		time="2026-02-06T21:29:35.390064982Z" l

from Python SDK PR here dapr/python-sdk#905

Run https://github.com/dapr/python-sdk/actions/runs/21765533432/job/62802954846?pr=905