Update astro monorepo

This PR contains the following updates:

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

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### Release Notes

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

### [`v6`](https://github.com/actions/checkout/compare/v5...v6)

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

</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.

---

 - [ ] <!-- 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:eyJjcmVhdGVkSW5WZXIiOiI0Mi41LjEiLCJ1cGRhdGVkSW5WZXIiOiI0Mi41LjEiLCJ0YXJnZXRCcmFuY2giOiJtYWluIiwibGFiZWxzIjpbXX0=-->

Reviewed-on: #90
Co-authored-by: Renovate Bot <renovate-bot@alexlebens.net>
Co-committed-by: Renovate Bot <renovate-bot@alexlebens.net>

.gitea/workflows/release-image.yml

@@ -12,7 +12,7 @@ jobs:
     runs-on: ubuntu-js
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Login to Registry
         uses: docker/login-action@v3

.gitea/workflows/renovate.yaml

@@ -16,7 +16,7 @@ jobs:
     container: ghcr.io/renovatebot/renovate:42
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Renovate
         run: renovate

.gitea/workflows/test-build.yaml

@@ -14,7 +14,7 @@ jobs:
     runs-on: ubuntu-js
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Set up pnpm
         uses: pnpm/action-setup@v4