ci/github-script/merge: improve wording

To ensure security and a focused utility, the bot adheres to specific limitations:

- The PR targets `master`, `staging`, or `staging-next`.

- The PR only touches files located under `pkgs/by-name/*`.

- The PR only touches packages located under `pkgs/by-name/*`.

- The PR is authored by [@r-ryantm](https://nix-community.github.io/nixpkgs-update/r-ryantm/) or a [committer][@NixOS/nixpkgs-committers].

- The user attempting to merge is a member of [@NixOS/nixpkgs-maintainers].

- The user attempting to merge is a maintainer of all packages touched by the PR.

      'staging',

      'staging-next',

    ].includes(pull_request.base.ref),

    'PR touches only files in `pkgs/by-name/`.': allByName,

    'PR touches only packages in `pkgs/by-name/`.': allByName,

    'PR authored by r-ryantm or committer.':

      pull_request.user.login === 'r-ryantm' ||

      committers.has(pull_request.user.id),

  }

  if (user) {

    checklist[`${user.login} can use the merge bot.`] = userIsMaintainer

    checklist[

      `${user.login} is a member of [@NixOS/nixpkgs-maintainers](https://github.com/orgs/NixOS/teams/nixpkgs-maintainers).`

    ] = userIsMaintainer

    if (allByName) {

      // We can only determine the below, if all packages are in by-name, since

      // we can't reliably relate changed files to packages outside by-name.

    const body = [

      `<!-- comment: ${comment.node_id} -->`,

      `@${comment.user.login} wants to merge this PR.`,

      '',

      'Requirements to merge this PR:',

      'Requirements to merge this PR with `@NixOS/nixpkgs-merge-bot merge`:',

      ...Object.entries(checklist).map(

        ([msg, res]) => `- :${res ? 'white_check_mark' : 'x'}: ${msg}`,

      ),