chore(deps): update actions/checkout action to v6 (#396)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [actions/checkout](https://github.com/actions/checkout) | action | major | `v5.0.1` -> `v6.0.0` |

---

### Release Notes

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

### [`v6.0.0`](https://github.com/actions/checkout/releases/tag/v6.0.0)

[Compare Source](https://github.com/actions/checkout/compare/v5.0.1...v6.0.0)

#### What's Changed

- Update README to include Node.js 24 support details and requirements by [@&#8203;salmanmkc](https://github.com/salmanmkc) in [#&#8203;2248](https://github.com/actions/checkout/pull/2248)
- Persist creds to a separate file by [@&#8203;ericsciple](https://github.com/ericsciple) in [#&#8203;2286](https://github.com/actions/checkout/pull/2286)
- v6-beta by [@&#8203;ericsciple](https://github.com/ericsciple) in [#&#8203;2298](https://github.com/actions/checkout/pull/2298)
- update readme/changelog for v6 by [@&#8203;ericsciple](https://github.com/ericsciple) in [#&#8203;2311](https://github.com/actions/checkout/pull/2311)

**Full Changelog**: <https://github.com/actions/checkout/compare/v5.0.0...v6.0.0>

</details>

---

### Configuration

📅 **Schedule**: Branch creation - At any time (no schedule defined), Automerge - At any time (no schedule defined).

🚦 **Automerge**: Disabled by config. Please merge this manually once you are satisfied.

♻ **Rebasing**: Whenever PR is behind base branch, or you tick the rebase/retry checkbox.

🔕 **Ignore**: Close this PR and you won't be reminded about this update again.

---

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---

This PR has been generated by [Renovate Bot](https://github.com/renovatebot/renovate).
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Reviewed-on: #396
Co-authored-by: renovate[bot] <renovate-bot@git.tainton.uk>
Co-committed-by: renovate[bot] <renovate-bot@git.tainton.uk>

.gitea/workflows/security.yml

@@ -25,7 +25,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout repo
-        uses: actions/checkout@v5.0.1
+        uses: actions/checkout@v6.0.0
 
       - name: Snyk
         uses: snyk/actions/python@master