Fix for private repos

[severinbratus]

Deploying a private repo requires a secret named GH_PAT with a PAT token with at least the scopes repo, read:org, gist (these scopes are listed here: https://cli.github.com/manual/gh_auth_login).

See also comment:

env:
  GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
  # Relevant and required for Private repositories only!
  # 1. First, create a Personal Access Token (Classic) as in https://docs.github.com/en/authentication/keeping-your-account-and-data-secure/managing-your-personal-access-tokens
  #    with at least the scopes `repo`, `read:org`, and `gist`.
  # 2. Then, make a secret GH_PAT in `Settings` > `Secrets and variables` > `Actions` > `Repository secrets` or `Organization secrets`.
  #    Copy & paste the PAT from step 1.
  #
  # Clarifications on naming:
  # GH_TOKEN is the name that the `gh` CLI utility expects.
  # GITHUB_TOKEN is a special automatically assigned token described here https://docs.github.com/en/actions/security-guides/automatic-token-authentication
  GH_TOKEN: ${{ secrets.GH_PAT != '' && secrets.GH_PAT || secrets.GITHUB_TOKEN }}
  

Tested at:

• (public) https://github.com/TeachBooks/testable-template/actions/runs/9537913471
• (private) https://github.com/TeachBooks/testable-template-private/actions/runs/9537272342

Resolves #32

[Tom-van-Woudenberg]

Wonderful!