Update actions/checkout action to v6 (#312)

This PR contains the following updates:

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

---

### Release Notes

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

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

[Compare Source](actions/checkout@v5...v6)

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

</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 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).
<!--renovate-debug:eyJjcmVhdGVkSW5WZXIiOiI0MS4xNDYuMCIsInVwZGF0ZWRJblZlciI6IjQxLjE0Ni4wIiwidGFyZ2V0QnJhbmNoIjoibWFpbiIsImxhYmVscyI6W119-->

Reviewed-on: https://git.walbeck.it/walbeck-it/docker-determine-docker-tags/pulls/312
Co-authored-by: renovate-bot <[email protected]>
Co-committed-by: renovate-bot <[email protected]>

Author: renovate-bot

.forgejo/workflows/build.yml

@@ -9,15 +9,15 @@ jobs:
   lint:
     runs-on: docker
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: https://github.com/hadolint/[email protected]
         with:
           dockerfile: Dockerfile
 
   build:
     runs-on: dind
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Get docker tags
         id: tags
         shell: sh

.forgejo/workflows/test.yml

@@ -7,15 +7,15 @@ jobs:
     if: github.ref != 'refs/heads/renovate/*'
     runs-on: docker
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: https://github.com/hadolint/[email protected]
         with:
           dockerfile: Dockerfile
 
   test:
     runs-on: dind
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Get docker tags
         id: tags
         shell: sh