If I add a `if __name__ == '__main__':` I get the same result.

Here's the gdb stack trace:

  #0  __futex_abstimed_wait_common64 (private=<optimized out>, cancel=true, abstime=0x0, op=393, expected=0, futex_word=0x17bc7c0) at ./nptl/futex-internal.c:57
  #1  __futex_abstimed_wait_common (cancel=true, private=<optimized out>, abstime=0x0, clockid=0, expected=0, futex_word=0x17bc7c0) at ./nptl/futex-internal.c:87
  #2  __GI___futex_abstimed_wait_cancelable64 (futex_word=futex_word@entry=0x17bc7c0, expected=expected@entry=0, clockid=clockid@entry=0, abstime=abstime@entry=0x0, 
    private=<optimized out>) at ./nptl/futex-internal.c:139
  #3  0x00007ff326c9cc5f in do_futex_wait (sem=sem@entry=0x17bc7c0, abstime=0x0, clockid=0) at ./nptl/sem_waitcommon.c:111
  #4  0x00007ff326c9ccf8 in __new_sem_wait_slow64 (sem=0x17bc7c0, abstime=0x0, clockid=0) at ./nptl/sem_waitcommon.c:183
  #5  0x00007ff326c9cd71 in __new_sem_wait (sem=<optimized out>) at ./nptl/sem_wait.c:42
  #6  0x000000000042765b in PyThread_acquire_lock_timed (lock=0x17bc7c0, microseconds=-1, intr_flag=0) at ../Python/thread_pthread.h:483
  #7  0x0000000000625813 in _enter_buffered_busy (self=0x7ff326f330f0) at ../Modules/_io/bufferedio.c:281
  #8  0x000000000045f9b3 in buffered_flush (self=0x7ff326f330f0, args=<optimized out>) at ../Modules/_io/bufferedio.c:825
  #9  0x0000000000524185 in method_vectorcall_NOARGS (func=func@entry=<method_descriptor at remote 0x7ff326f611d0>, args=args@entry=0x7fffa8bc7a38, nargsf=<optimized out>, 
    kwnames=kwnames@entry=0x0) at ../Objects/descrobject.c:436
  #10 0x000000000053bd5a in _PyObject_VectorcallTstate (kwnames=0x0, nargsf=<optimized out>, args=0x7fffa8bc7a38, callable=<method_descriptor at remote 0x7ff326f611d0>, 
    tstate=0x17bf410) at ../Include/cpython/abstract.h:118
  #11 PyObject_VectorcallMethod (name=<optimized out>, args=0x7fffa8bc7a38, nargsf=<optimized out>, kwnames=0x0) at ../Objects/call.c:828
  #12 0x000000000060283a in _PyObject_CallMethodIdNoArgs (name=0x8f6120 <PyId_flush.lto_priv.2>, self=<optimized out>) at ../Include/cpython/abstract.h:243
  #13 _io_TextIOWrapper_flush_impl (self=0x7ff326f40040) at ../Modules/_io/textio.c:3038
  #14 _io_TextIOWrapper_flush (self=0x7ff326f40040, _unused_ignored=<optimized out>) at ../Modules/_io/clinic/textio.c.h:685