Fix the incorrect type error in unbounded Python UDAF

Caused by: java.util.concurrent.ExecutionException: java.lang.RuntimeException: Error received from SDK harness for instruction 1: Traceback (most recent call last):
  File "/usr/local/python3/lib/python3.7/site-packages/apache_beam/runners/worker/sdk_worker.py", line 289, in _execute
    response = task()
  File "/usr/local/python3/lib/python3.7/site-packages/apache_beam/runners/worker/sdk_worker.py", line 362, in <lambda>
    lambda: self.create_worker().do_instruction(request), request)
  File "/usr/local/python3/lib/python3.7/site-packages/apache_beam/runners/worker/sdk_worker.py", line 607, in do_instruction
    getattr(request, request_type), request.instruction_id)
  File "/usr/local/python3/lib/python3.7/site-packages/apache_beam/runners/worker/sdk_worker.py", line 644, in process_bundle
    bundle_processor.process_bundle(instruction_id))
  File "/usr/local/python3/lib/python3.7/site-packages/apache_beam/runners/worker/bundle_processor.py", line 1000, in process_bundle
    element.data)
  File "/usr/local/python3/lib/python3.7/site-packages/apache_beam/runners/worker/bundle_processor.py", line 228, in process_encoded
    self.output(decoded_value)
  File "apache_beam/runners/worker/operations.py", line 357, in apache_beam.runners.worker.operations.Operation.output
  File "apache_beam/runners/worker/operations.py", line 359, in apache_beam.runners.worker.operations.Operation.output
  File "apache_beam/runners/worker/operations.py", line 221, in apache_beam.runners.worker.operations.SingletonConsumerSet.receive
  File "pyflink/fn_execution/beam/beam_operations_fast.pyx", line 71, in pyflink.fn_execution.beam.beam_operations_fast.FunctionOperation.process
  File "pyflink/fn_execution/beam/beam_operations_fast.pyx", line 84, in pyflink.fn_execution.beam.beam_operations_fast.FunctionOperation.process
  File "/usr/local/python3/lib/python3.7/site-packages/pyflink/fn_execution/operations.py", line 115, in process_element
    return self.func(value)
  File "/usr/local/python3/lib/python3.7/site-packages/pyflink/fn_execution/operations.py", line 384, in process_element_or_timer
    self.group_agg_function.on_timer(input_data[3])
TypeError: Argument 'key' has incorrect type (expected pyflink.fn_execution.coder_impl_fast.InternalRow, got Row)

	at java.util.concurrent.CompletableFuture.reportGet(CompletableFuture.java:357)
	at java.util.concurrent.CompletableFuture.get(CompletableFuture.java:1895)
	at org.apache.beam.sdk.util.MoreFutures.get(MoreFutures.java:60)
	at org.apache.beam.runners.fnexecution.control.SdkHarnessClient$BundleProcessor$ActiveBundle.close(SdkHarnessClient.java:504)
	at org.apache.beam.runners.fnexecution.control.DefaultJobBundleFactory$SimpleStageBundleFactory$1.close(DefaultJobBundleFactory.java:555)
	at org.apache.flink.streaming.api.runners.python.beam.BeamPythonFunctionRunner.finishBundle(BeamPythonFunctionRunner.java:381)