Trying to sync 2 private repos using this github action. I cannot use a personal access token.
For the looks of if I don't have access to the source repo when running the workflow using the github-sync action.

UPSTREAM_REPO does not seem to be a valid git URI, assuming it's a GitHub repo
Originally: {owner}/{repo-name}
Now: https://github.com/{owner}/{repo-name}.git // this repo exists
UPSTREAM_REPO=https://github.com/{owner}/{repo-name}.git // this repo exists
BRANCHES=master:master-test
Resetting origin to: ***github.com/{owner}/{anohter-repo-name} // this repo exists
Adding tmp_upstream https://github.com/{owner}/{repo-name}.git
Fetching tmp_upstream
fatal: could not read Username for 'https://github.com/': No such device or address

I've also tried both ways recommended in the README for accessing the repo, including the ssh key without any luck. Can you please help?

If source_repo is private or with another provider, either (1) use an authenticated HTTPS repo clone url like https://${access_token}@github.com/owner/repository.git or (2) set a SSH_PRIVATE_KEY secret environment variable and use the SSH clone url