[issue21120] PyArena type is used in headers from the limited API

[Zackery Spytz]

Change by Zackery Spytz <zspytz at gmail.com>:


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components: +Build -Library (Lib)
nosy: +ZackerySpytz
versions: +Python 3.9 -Python 3.5

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue21120>
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