[issue28796] FIX warnings in documentation build

[Julien Palard]

Changes by Julien Palard <julien+python at palard.fr>:


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assignee:  -> docs at python
components: +Documentation
nosy: +docs at python
versions: +Python 3.7

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue28796>
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