Hey there,
I just have learned something about Git and GitHub. When I get it correctly, GitHub is a server, respectively a company, where source codes of projects like bitcoin are hosted, right? What about the company? Don’t we have to trust them, as they are hosting the source code? The source code isn’t stored decentrally, is it?
Hope someone can help me.
To my understanding, even though GitHub is hosting source code, it is not running the source code. Also, those who wrote code, whether for their own portfolio or for a company, are going to have backups. So if GitHub were to alter the code, the creators of it would take notice.
That is my best understanding anyway. Hope this helps 
Pretty much what I meant aswell. Besides there are other services such as GitLab or BitBucket. It is essential for developers to have their offline copy.
Thanks @Mauro & @Harmony you could already helped me.
I would like to figure out the worst case scenario which can happen to bitcoin as it is hosted by GitHub, if there is such a bad scenario. And her is my next question. Can you even say it like that?: “Bitcoin is hosted by GitHub (Microsoft) but run by the community.” As the source code is on GitHub while the blockchain is running on different computer (Nodes).
Who at the end is able to change the source code? Probably some developers with administration rights, right?
@Paultier Github is only displaying the source code. Github could delete it and the Bitcoin blockchain would still run. As far as I understand, correct me anyone if I’m wrong here, but anyone can take the source code and make their own blockchain from it. All that would happen is another blockchain with another cryptocurrency would be published. Ever heard of an Ethereum based crypto? That’s cause they used Ethereum’s source code to start their project. The same concept is true for Bitcoin.
It takes community consensus to alter the source code of a blockchain. That is why forks happen; not everyone agrees on the change that is proposed. This is where Bitcoin Cash came from (if I remember correctly), it was a fork off of Bitcoin. Not everyone agreed to the change being made to the code, so it split into the two.
Hope this clarifies some things for you 