Fixed GitHub status API and access to the pull requests of private projects

[StudioMaX]

There are two fixes for GitHub-hosted repositories:

1. There was a typo due to which the status API was broken ob GitHub (31f9232#diff-7e0d0931800d0b6846f60da0d2b19cd6)
2. When working with PR on GitHub the repository is downloaded in a special way:

• At first, the main project's repository is downloaded
• Then a new branch is created with the changes from PR, which are located in the forked repository.

If both of these projects (original and fork) are private, then they should be downloaded using a ssh-key. The issue was that when downloading the fork, this ssh-key was not used.
Therefore it worked with public repositories, but did not work with private ones.

[corpsee]

Thanks @StudioMaX! I will try to review soon.