[docs] [issue30619] typing.Union doc incoherence in case a class and its subclass are present

[Mariatta Wijaya]

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


----------
pull_requests: +2380

_______________________________________
Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue30619>
_______________________________________