In the _interpreters module, we use PyEval_EvalCode() to run Python code in another interpreter. However, when the process receives a KeyboardInterrupt, PyEval_EvalCode() will jump straight to finalization rather than returning. This prevents us from cleaning up and marking the thread as "not running main", which triggers an assertion in PyThreadState_Clear() on debug builds. Since everything else works as intended, remove that assertion.
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