fix(fr): align /arckit:fr-irn with the IRN v1.2 grid - #911

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: DavidAnson/markdownlint-cli2-action@992badcdf24e3b8eb7e87ff9287fe931bcb00c6e. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/