doc: Add deprecation warning to catch Expr - #11436

Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: erlef/setup-beam@e6d7c94229049569db56a7ad5a540c051a010af9. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/