I have a doubt... suppose a company one day decides to save all the code of their project on github, even if it is a private repository don't you risk sharing sensitive information that could compromise the entire project? (I am still referring to a free account without any upgrades or such things)
If this is the perception you have on GitHub or any other provider, you will have to do a local deployment in your infrastructure. In this way, you have to put extra effort for maintenance and updates and you will lose all the benefits that GitHub provides.
Anyway as a practice sensitive information such as credentials is not stored in git.