Update actions/checkout action to v5 (#13)

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This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [actions/checkout](https://redirect.github.com/actions/checkout) |
action | major | `v4` -> `v5` |

---

### Release Notes

<details>
<summary>actions/checkout (actions/checkout)</summary>

### [`v5`](https://redirect.github.com/actions/checkout/compare/v4...v5)

[Compare
Source](https://redirect.github.com/actions/checkout/compare/v4...v5)

</details>

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---

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.github/workflows/jekyll.yml

@@ -32,7 +32,7 @@ jobs:
     runs-on: ubuntu-24.04
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v5
       - name: Setup Ruby
         uses: ruby/setup-ruby@v1.233.0
         with: