[Failing Test]: :sdks:python:test-suites:tox:py39:testPython39 can be flaky

[liferoad]

What happened?

Task :sdks:python:test-suites:tox:py39:testPython39 FAILED

https://github.com/apache/beam/actions/runs/15515806611/job/43682530543?pr=34329#step:8:6211

Flaky with

apache_beam/runners/portability/portable_runner_test.py::PortableRunnerTest::test_assert_that
  /runner/_work/beam/beam/sdks/python/test-suites/tox/py39/build/srcs/sdks/python/target/.tox-py39-cloud/py39-cloud/lib/python3.9/site-packages/_pytest/threadexception.py:73: PytestUnhandledThreadExceptionWarning: Exception in thread Thread-35
  
  Traceback (most recent call last):
    File "apache_beam/runners/common.py", line 1498, in apache_beam.runners.common.DoFnRunner.process
      return self.do_fn_invoker.invoke_process(windowed_value)
    File "apache_beam/runners/common.py", line 912, in apache_beam.runners.common.PerWindowInvoker.invoke_process
      self._invoke_process_per_window(
    File "apache_beam/runners/common.py", line 1057, in apache_beam.runners.common.PerWindowInvoker._invoke_process_per_window
      self.process_method(*args_for_process, **kwargs_for_process),
    File "/runner/_work/beam/beam/sdks/python/test-suites/tox/py39/build/srcs/sdks/python/target/.tox-py39-cloud/py39-cloud/lib/python3.9/site-packages/apache_beam/transforms/core.py", line 2084, in <lambda>
      wrapper = lambda x, *args, **kwargs: [fn(x, *args, **kwargs)]
    File "/runner/_work/beam/beam/sdks/python/test-suites/tox/py39/build/srcs/sdks/python/target/.tox-py39-cloud/py39-cloud/lib/python3.9/site-packages/apache_beam/testing/util.py", line 200, in _equal
      raise BeamAssertException(msg)
  apache_beam.testing.util.BeamAssertException: Failed assert: ['a'] == ['a', 'b'], unexpected elements ['b']

Issue Failure

Failure: Test is flaky

Issue Priority

Priority: 1 (unhealthy code / failing or flaky postcommit so we cannot be sure the product is healthy)

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