fix e2e TestSecurityRollingUpgrade.test_rolling_upgrade_sasl_mechanism_phase_one

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SESSION REPORT (ALL TESTS)
ducktape version: 0.12.0
session_id:       2024-12-16--001
run time:         5 minutes 55.742 seconds
tests run:        1
passed:           0
flaky:            0
failed:           1
ignored:          0
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test_id:    kafkatest.tests.core.security_rolling_upgrade_test.TestSecurityRollingUpgrade.test_rolling_upgrade_sasl_mechanism_phase_one.new_client_sasl_mechanism=PLAIN.metadata_quorum=ISOLATED_KRAFT
status:     FAIL
run time:   5 minutes 55.502 seconds

TimeoutError('Expected producer to still be producing.')
Traceback (most recent call last):
File "/usr/local/lib/python3.7/dist-packages/ducktape/tests/runner_client.py", line 351, in _do_run
data = self.run_test()
File "/usr/local/lib/python3.7/dist-packages/ducktape/tests/runner_client.py", line 411, in run_test
return self.test_context.function(self.test)
File "/usr/local/lib/python3.7/dist-packages/ducktape/mark/_mark.py", line 438, in wrapper
return functools.partial(f, *args, **kwargs)(*w_args, **w_kwargs)
File "/opt/kafka-dev/tests/kafkatest/tests/core/security_rolling_upgrade_test.py", line 140, in test_rolling_upgrade_sasl_mechanism_phase_one
self.run_produce_consume_validate(self.add_sasl_mechanism, new_client_sasl_mechanism)
File "/opt/kafka-dev/tests/kafkatest/tests/produce_consume_validate.py", line 107, in run_produce_consume_validate
self.stop_producer_and_consumer()
File "/opt/kafka-dev/tests/kafkatest/tests/produce_consume_validate.py", line 95, in stop_producer_and_consumer
self.check_producing()
File "/opt/kafka-dev/tests/kafkatest/tests/produce_consume_validate.py", line 91, in check_producing
err_msg="Expected producer to still be producing.")
File "/usr/local/lib/python3.7/dist-packages/ducktape/utils/util.py", line 58, in wait_until
raise TimeoutError(err_msg() if callable(err_msg) else err_msg) from last_exception
ducktape.errors.TimeoutError: Expected producer to still be producing.

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