chore(deps): update actions/checkout action to v6 (#54)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [actions/checkout](https://github.com/actions/checkout) | action | major | `v4` -> `v6` |

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> ⚠️ **Warning**
>
> Some dependencies could not be looked up. Check the Dependency Dashboard for more information.

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### Release Notes

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

### [`v6`](https://github.com/actions/checkout/blob/HEAD/CHANGELOG.md#v600)

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

- Persist creds to a separate file by [@&#8203;ericsciple](https://github.com/ericsciple) in [#&#8203;2286](https://github.com/actions/checkout/pull/2286)
- 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)

### [`v5`](https://github.com/actions/checkout/blob/HEAD/CHANGELOG.md#v501)

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

- Port v6 cleanup to v5 by [@&#8203;ericsciple](https://github.com/ericsciple) in [#&#8203;2301](https://github.com/actions/checkout/pull/2301)

</details>

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### Configuration

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This PR has been generated by [Renovate Bot](https://github.com/renovatebot/renovate).
<!--renovate-debug:eyJjcmVhdGVkSW5WZXIiOiI0MS4xNjkuMyIsInVwZGF0ZWRJblZlciI6IjQyLjI0LjAiLCJ0YXJnZXRCcmFuY2giOiJtYWluIiwibGFiZWxzIjpbXX0=-->

Co-authored-by: Renovate Bot <bot@renovateapp.com>
Reviewed-on: https://codeberg.org/tmayoff/.dotfiles/pulls/54

.forgejo/workflows/main.yml

@@ -23,7 +23,7 @@ jobs:
     runs-on: kaylee
     continue-on-error: false
     steps:
-    - uses: actions/checkout@v4
+    - uses: actions/checkout@v6
 
     - name: Install Nix
       uses: https://github.com/DeterminateSystems/nix-installer-action@main

.forgejo/workflows/renovate.yml

@@ -15,7 +15,7 @@ jobs:
 
     steps:
       - name: Checkout
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: Install Nix
         uses: https://github.com/DeterminateSystems/nix-installer-action@main