[docs] [issue30335] Document deprecated alias of assertNotRegex

[Mariatta Wijaya]

Changes by Mariatta Wijaya <mariatta.wijaya at gmail.com>:


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assignee:  -> docs at python
components: +Documentation -Tests
nosy: +docs at python
stage:  -> backport needed
versions: +Python 3.5, Python 3.6

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue30335>
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