The https://github.com/robots.txt file of GitHub allows the indexing of the blobs in the ‘master’ branch, but restricts all other branches. So if you don’t have a ‘master’ branch, Google is not supposed to index your pages.
How to remove the ‘master’ branch:
In your clone create a new branch – let’s call it ‘main’ and push it to GitHub
git checkout -b main
git push -u origin main
On GitHub change the default branch (see in the Settings section of your repository)
or here https://github.com/blog/421-pick-your-default-branch
Then remove the master branch from your clone and from GitHub:
git branch -d master
git push origin :master
Get other people who might have already forked your repository to do the same.
Alternatively, if you’d like to financially support GitHub, you can go private https://help.github.com/articles/making-a-public-repository-private