gh-48330: assert warning is emitted on unittest.TestResult with no addDuration

[iritkatriel]

Fixes the warning below, which started with #12271.

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ERROR: test_run_call_order_default_result (test.test_unittest.test_case.Test_TestCase.test_run_call_order_default_result)
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AttributeError: 'ResultWithNoStartTestRunStopTestRun' object has no attribute 'addDuration'
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "/Users/iritkatriel/src/cpython/Lib/test/test_unittest/test_case.py", line 307, in test_run_call_order_default_result
Foo('test').run()
File "/Users/iritkatriel/src/cpython/Lib/unittest/case.py", line 639, in run
self._addDuration(result, (time.perf_counter() - start_time))
File "/Users/iritkatriel/src/cpython/Lib/unittest/case.py", line 580, in _addDuration
warnings.warn("TestResult has no addDuration method",
RuntimeWarning: TestResult has no addDuration method

• Issue: unittest: display time used by each test case #48330

[giampaolo]

Thanks. LGTM.