Prevent @react-native-bot from double posting on missing reproducer (#47427)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/47427

I've noticed that react-native-bot posts twice once we can't find a reproducer.
(see here: https://github.com/facebook/react-native/issues/47421)

This fixes it by letting it post only once.

Changelog:
[Internal] [Changed] - Prevent react-native-bot from double posting on missing reproducer

Reviewed By: mdvacca

Differential Revision: D65485634

fbshipit-source-id: dbe9b1311aef246dead6d9b922c1256363e894f7