You can change the shell for the git user to git-shell, which will prevent them from running anything but git commands (As far as I'm aware that's all GitHub does on their servers).
If you're after something that doesn't give devs access to certain repos, you can always symlink like Håvard Pedersen mentioned; although if you're wanting something like that, you're probably better off with a solution like GitLab anyway.
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You can change the shell for the git user to git-shell, which will prevent them from running anything but git commands (As far as I'm aware that's all GitHub does on their servers).
If you're after something that doesn't give devs access to certain repos, you can always symlink like Håvard Pedersen mentioned; although if you're wanting something like that, you're probably better off with a solution like GitLab anyway.