If `HOMEBREW_GITHUB_API_TOKEN` is not set and `GITHUB_TOKEN` is: let's use it. `GITHUB_TOKEN` is a somewhat standard env var to set for GitHub authentication tokens (e.g. used by `hub`).
If `HOMEBREW_GITHUB_API_TOKEN` is not set and `GITHUB_TOKEN` is: let's use it. `GITHUB_TOKEN` is a somewhat standard env var to set for GitHub authentication tokens (e.g. used by `hub`).