gh-120321: Fix TSan reported race in gen_clear_frame

[colesbury]

TSan treats compare-exchanges that fail as if they are writes so there is a false positive with the read of gi_frame_state in gen_close.

• Issue: SIGSEGV with generators in free-threaded build #120321

[colesbury]

I keep making this same mistake. This Should fix https://github.com/python/cpython/actions/runs/20383044472/job/58577900039?pr=142957:

WARNING: ThreadSanitizer: data race (pid=21767) Read of size 1 at 0x7f9ccb6ceb63 by thread T475: #0 gen_clear_frame /home/runner/work/cpython/cpython/Objects/genobject.c:156:5 (python+0x2afcde) (BuildId: edcf083ae7c4567c86d1e5be11648e5caf6d5047) #1 gen_close /home/runner/work/cpython/cpython/Objects/genobject.c (python+0x2ac1d1) (BuildId: edcf083ae7c4567c86d1e5be11648e5caf6d5047) #2 method_vectorcall_NOARGS /home/runner/work/cpython/cpython/Objects/descrobject.c:448:24 (python+0x289784) (BuildId: edcf083ae7c4567c86d1e5be11648e5caf6d5047) #3 _PyObject_VectorcallTstate /home/runner/work/cpython/cpython/./Include/internal/pycore_call.h:136:11 (python+0x26a6ab) (BuildId: edcf083ae7c4567c86d1e5be11648e5caf6d5047) ... Previous atomic write of size 1 at 0x7f9ccb6ceb63 by thread T472: #0 _Py_atomic_compare_exchange_int8 /home/runner/work/cpython/cpython/./Include/cpython/pyatomic_gcc.h:75:10 (python+0x2b0751) (BuildId: edcf083ae7c4567c86d1e5be11648e5caf6d5047) #1 gen_send_ex /home/runner/work/cpython/cpython/Objects/genobject.c:327:15 (python+0x2b0751) #2 gen_iternext /home/runner/work/cpython/cpython/Objects/genobject.c:720:9 (python+0x2acf7c) (BuildId: edcf083ae7c4567c86d1e5be11648e5caf6d5047) #3 _PyForIter_VirtualIteratorNext /home/runner/work/cpython/cpython/Python/ceval.c:4056:24 (python+0x520502) (BuildId: edcf083ae7c4567c86d1e5be11648e5caf6d5047) #4 _PyEval_EvalFrameDefault /home/runner/work/cpython/cpython/Python/generated_cases.c.h:5500:36 (python+0x4f33f8) (BuildId: edcf083ae7c4567c86d1e5be11648e5caf6d5047)