Update GitHub Actions versions

[lydell]

CI failed in #254:

Run mpizenberg/elm-tooling-action@v1.7
(node:1169) [DEP0040] DeprecationWarning: The `punycode` module is deprecated. Please use a userland alternative instead.
(Use `node --trace-deprecation ...` to show where the warning was created)
/Users/runner/work/test/test/elm-tooling.json

tools["elm"]
    Unknown version: 0.19.2
Error: Failed to install tools
    Known versions: 0.19.0, 0.19.1

Also there is this warning:

Node 20 is being deprecated. This workflow is running with Node 24 by default. If you need to temporarily use Node 20, you can set the ACTIONS_ALLOW_USE_UNSECURE_NODE_VERSION=true environment variable. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

This PR updates all actions to the latest version, which fixes the above problems.