Update `actions/checkout` in GitHub Actions workflow

[ptgolden]

I've been seeing these warnings under GitHub Actions workflows that use actions/checkout@v4 (which is used in https://github.com/INCATools/odkcore/blob/main/src/incatools/odk/templates/_dynamic_workflows.jinja2):

Node.js 20 actions are deprecated. The following actions are running on Node.js 20 and may not work as expected: actions/checkout@v4. Actions will be forced to run with Node.js 24 by default starting June 2nd, 2026. Node.js 20 will be removed from the runner on September 16th, 2026. Please check if updated versions of these actions are available that support Node.js 24. To opt into Node.js 24 now, set the FORCE_JAVASCRIPT_ACTIONS_TO_NODE24=true environment variable on the runner or in your workflow file. Once Node.js 24 becomes the default, you can temporarily opt out by setting ACTIONS_ALLOW_USE_UNSECURE_NODE_VERSION=true. For more information see: https://github.blog/changelog/2025-09-19-deprecation-of-node-20-on-github-actions-runners/

The fix should be as easy as updating to actions/checkout@v6, but it seems like current workflows will stop working without intervention on June 2 (!)

[gouttegd]

Updating the ODK template to use actions/checkout@v6 is trivial (will do that soon), but I wonder if we should have a more future-proof mechanism.

The problem is that even if the upcoming ODK 1.7 generates workflow files that use actions/checkout@v6, that action may also become obsolete before we get to ODK 1.8.

So maybe the templating system should be slightly “smarter” and automatically determine what is the latest version of actions/checkout at the time the template is instantiated?

[ptgolden]

Yeah, that might be best.

One thing particular about how actions are published is that you might not necessarily want the "latest release". The latest release of actions/checkout at the moment is v6.0.2, but I think the expectation might be wanting v6. Both point to the same commit right now, but if v6.0.3 gets released, v6 will be re-published to point to the commit of that tag. There are no actual semantics in actions to resolve semver, it's just this convention.

[ptgolden]

Another option might be to add a default workflow to use dependabot to monitor updates to GitHub actions? That way it would take care of updates outside of the lifecycle events of "set up repository" and "update ODK version". It's pretty GitHub-specific, but then again, so are GitHub workflows.