fetchFromGitHub: use of the API endpoint only when fetching tarball (#388166)

    else fetchzip;

  privateAttrs = lib.optionalAttrs private {

    netrcPhase =

      let machineName = if githubBase == "github.com" then "api.github.com" else githubBase;

      # When using private repos:

      # - Fetching with git works using https://github.com but not with the GitHub API endpoint

      # - Fetching a tarball from a private repo requires to use the GitHub API endpoint

      let machineName = if githubBase == "github.com" && !useFetchGit then "api.github.com" else githubBase;

      in ''

        if [ -z "''$${varBase}USERNAME" -o -z "''$${varBase}PASSWORD" ]; then

          echo "Error: Private fetchFromGitHub requires the nix building process (nix-daemon in multi user mode) to have the ${varBase}USERNAME and ${varBase}PASSWORD env vars set." >&2