[docs] [issue29239] Fix wrong issue number in what's new entry

[Roundup Robot]

New submission from Roundup Robot:

New changeset 114b03fa4c04 by Martin Panter in branch '3.6':
Issue #29239: Fix --enable-optimizations bug number
https://hg.python.org/cpython/rev/114b03fa4c04

New changeset 4e29c7f2b3e5 by Martin Panter in branch 'default':
Issue #29239: Merge bug number from 3.6
https://hg.python.org/cpython/rev/4e29c7f2b3e5

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nosy: +python-dev

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue29239>
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