[CI] Cron job workflow to run `test-and-fix` and commit results

[chalin]

We should consider setting up a workflow to execute npm run test-and-fix and commit results, so as to minimize the likelihood of our contributors being told to keep their PRs focused to their own changes, like #6585 (comment). /cc @svrnm

[chalin]

Actually, as discussed on Slack, let's run the i18n checks on every PR instead.