chore(deps): update https://code.forgejo.org/actions/checkout action to v5 (#217)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [https://code.forgejo.org/actions/checkout](https://code.forgejo.org/actions/checkout) | action | major | `v4` -> `v5` |

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### Release Notes

<details>
<summary>actions/checkout (https://code.forgejo.org/actions/checkout)</summary>

### [`v5`](https://code.forgejo.org/actions/checkout/compare/v4...v5)

[Compare Source](https://code.forgejo.org/actions/checkout/compare/v4...v5)

</details>

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### 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 becomes conflicted, or you tick the rebase/retry checkbox.

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

---

 - [ ] <!-- rebase-check -->If you want to rebase/retry this PR, check this box

---

This PR has been generated by [Renovate Bot](https://github.com/renovatebot/renovate).
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Reviewed-on: https://git.nadeko.net/Fijxu/invidious/pulls/217
Co-authored-by: Renovate Bot <git@nadeko.net>
Co-committed-by: Renovate Bot <git@nadeko.net>

.forgejo/workflows/ci.yml

@@ -21,7 +21,7 @@ jobs:
     runs-on: runner
 
     steps:
-      - uses: https://code.forgejo.org/actions/checkout@v4
+      - uses: https://code.forgejo.org/actions/checkout@v5
 
       - uses: https://code.forgejo.org/docker/setup-buildx-action@v3
         name: Setup Docker BuildX system