Bump actions/checkout off the deprecated v4 in @danielridgebot's workflows

### Overview

We need to bump `actions/checkout` from `v4` to `v5` in all four of @danielridgebot's workflows, because v4 targets Node.js 20 and GitHub is force-running it on Node 24 on every run — when that fallback is withdrawn the workflows break, and this bot's failure mode is silence rather than an alert.

### Action Items

The bot's code lives in [hackforla/check-ghpages-versions](https://github.com/hackforla/check-ghpages-versions) — the org repo, not a personal account (the `danielridgebot/check-ghpages-versions` URL still resolves, but only as a redirect). The fix is one line per file, delivered as a PR on that repo.

- [ ] Bump `actions/checkout@v4` to `actions/checkout@v5` in all four workflows: `check-gh-pages-version.yml:13`, `check-ruby-version.yml:13`, `keepalive.yml:16`, `test-issue-labels.yml:11`. Line numbers were accurate 2026-08-24 and may drift — find them by the `uses: actions/checkout` line.
- [ ] Leave `actions/github-script@v8` alone (line 44 of both check workflows). It already runs on Node 24 and produces no annotation.
- [ ] Do not go past v5 in this pass, even though v7 is current. v5 is the pure Node 24 bump with no behaviour change. v6 moved the persisted git credential into a separate file, and three of these four workflows depend on that credential to `git push` a commit back to the repo. v7 additionally blocks fork checkouts for `pull_request_target`/`workflow_run`. Both are probably fine here, but neither is a one-line change any more — going current is a separate ticket that needs a real push test.
- [ ] Run `keepalive.yml` on the branch via `workflow_dispatch` and confirm the checkout step succeeds with no Node 20 annotation. It is safe to run at any time: it prints the repo's idle age and exits 0 without committing unless the repo has been idle 50 or more days.
- [ ] After the PR merges, confirm a scheduled run of `check-gh-pages-version.yml` or `check-ruby-version.yml` completes with no "Node.js 20 is deprecated" annotation. Both run daily (12:00 and 12:15 UTC), so this is a next-day check — it cannot be observed from the branch, because the annotation only appears on the runs that actually do the version check.

### Resources/Instructions

- Bot repo: https://github.com/hackforla/check-ghpages-versions — workflows are in `.github/workflows/`.
- Example of the annotation: https://github.com/hackforla/check-ghpages-versions/actions/runs/32782593141 (`check-ruby-version`, 2026-08-24) — _"Node.js 20 is deprecated. The following actions target Node.js 20 but are being forced to run on Node.js 24: actions/checkout@v4"_.
- Release notes, for the version reasoning above: [v5.0.0](https://github.com/actions/checkout/releases/tag/v5.0.0) (Node 24; requires runner v2.327.1+, which GitHub-hosted runners are well past), [v6.0.0](https://github.com/actions/checkout/releases/tag/v6.0.0), [v7.0.0](https://github.com/actions/checkout/releases/tag/v7.0.0).
- A full end-to-end test exists but has side effects and is **not** needed for this change: setting `release-versions/github-pages-gem.txt` to an older value and dispatching `check-gh-pages-version.yml` exercises the `git push` path, but it also opens a **real issue on hackforla/devops** with a board card, which then has to be closed and the card deleted.
- Related: #180 (re-enabled the bot's disabled workflow and added the keepalive).

In hackforla/check-ghpages-versions, inspect .github/workflows/check-gh-pages-version.yml, check-ruby-version.yml, keepalive.yml, and test-issue-labels.yml. Find each uses: actions/checkout entry and update only the four requested versions, then run keepalive.yml via workflow_dispatch. Done means checkout succeeds without a Node 20 annotation; a scheduled version-check run should be confirmed after the merge.

Scritto dal modello di indicizzazione a partire dal testo della issue.