Re-format once erlfmt supports OTP 27+

[paulo-ferraz-oliveira]

At the moment, we're not formatting src or test or ..., because erlfmt crashes (WhatsApp/erlfmt#355). Wait until a new OTP 27 -ready version comes out and reapply it, i.e. add fmt as the first element in list

{alias, [
    {ci, [

in rebar.config.

---

Also add

      - name: Check file format
        run: |
          rebar3 fmt --check

to ci.yml, before "Continuous Integration".