test_corrupted_file test flaky

Looks like a flake:

https://builds.apache.org/job/beam_PreCommit_Python_Commit/7924/consoleFull

11:22:24
11:22:24 ======================================================================
11:22:24 ERROR: test_corrupted_file (apache_beam.io.avroio_test.TestFastAvro)
11:22:24 ----------------------------------------------------------------------
11:22:24 Traceback (most recent call last):
11:22:24 File "/home/jenkins/jenkins-slave/workspace/beam_PreCommit_Python_Commit/src/sdks/python/test-suites/tox/py36/build/srcs/sdks/python/apache_beam/io/avroio_test.py", line 380, in test_corrupted_file
11:22:24 self.assertEqual(0, exn.exception.message.find('Unexpected sync marker'))
11:22:24 AttributeError: '_AssertRaisesContext' object has no attribute 'exception'
11:22:24 -------------------- >> begin captured logging << --------------------
11:22:24 apache_beam.io.filesystem: DEBUG: translate_pattern: '/tmp/tmpckgw8mk6' -> '\\/tmp
/tmpckgw8mk6'
11:22:24 --------------------- >> end captured logging << ---------------------
11:22:24
11:22:24 ----------------------------------------------------------------------
11:22:24 XML: /home/jenkins/jenkins-slave/workspace/beam_PreCommit_Python_Commit/src/sdks/python/test-suites/tox/py36/build/srcs/sdks/python/nosetests.xml
11:22:24 ----------------------------------------------------------------------
11:22:24 Ran 2455 tests in 1297.267s
11:22:24
11:22:24 FAILED (SKIP=546, errors=1)
11:22:24 ERROR: InvocationError for command /home/jenkins/jenkins-slave/workspace/beam_PreCommit_Python_Commit/src/sdks/python/test-suites/tox/py36/build/srcs/sdks/python/target/.tox-py36/py36/bin/python setup.py nosetests (exited with code 1)
11:22:24 py36 run-test-post: commands[0] | /home/jenkins/jenkins-slave/workspace/beam_PreCommit_Python_Commit/src/sdks/python/test-suites/tox/py36/build/srcs/sdks/python/scripts/run_tox_cleanup.sh
11:22:24 ___________________________________ summary ____________________________________
11:22:24 ERROR: py36: commands failed
11:22:24