[issue40204] Docs build error with Sphinx 3.0 due to invalid C declaration

[Ned Deily]

Change by Ned Deily <nad at python.org>:


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pull_requests: +20306
pull_request: https://github.com/python/cpython/pull/21147

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue40204>
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