Update sync_version.po: add ru description of the add_sticker_to_set method()

[E-Kozyreva]

Description

The ru documentation did not add a translation to the add_sticker_to_set() method. Therefore, I added the translation to sync_version.po description of the method in ru doc. url: https://pytba.readthedocs.io/ru/latest/sync_version/index.html#telebot.TeleBot.add_sticker_to_set

[coder2020official]

I need to update strings first