chore(deps): update docker/login-action action to v4 (#64)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [docker/login-action](https://github.com/docker/login-action) | action | major | `v3` → `v4` |

---

### Release Notes

<details>
<summary>docker/login-action (docker/login-action)</summary>

### [`v4`](https://github.com/docker/login-action/compare/v3...v4)

[Compare Source](https://github.com/docker/login-action/compare/v3...v4)

</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:eyJjcmVhdGVkSW5WZXIiOiI0My41Mi4wIiwidXBkYXRlZEluVmVyIjoiNDMuNTIuMCIsInRhcmdldEJyYW5jaCI6Im1haW4iLCJsYWJlbHMiOlsidHlwZS9kZXBlbmRlbmNpZXMiXX0=-->

Reviewed-on: #64
Co-authored-by: renovate[bot] <renovate-bot@git.tainton.uk>
Co-committed-by: renovate[bot] <renovate-bot@git.tainton.uk>

.gitea/workflows/build-push-docker.yml

@@ -52,14 +52,14 @@ jobs:
         uses: docker/setup-buildx-action@v3
 
       - name: Log in to Gitea Container Registry
-        uses: docker/login-action@v3
+        uses: docker/login-action@v4
         with:
           registry: ${{ inputs.registry }}
           username: ${{ inputs.actions_username }}
           password: ${{ secrets.ACTIONS_TOKEN }}
 
       - name: Log in to GitHub Container Registry
-        uses: docker/login-action@v3
+        uses: docker/login-action@v4
         with:
           registry: ghcr.io
           username: ${{ inputs.ghcr_username }}

.github/workflows/build-push-attest-docker.yml

@@ -32,7 +32,7 @@ jobs:
         uses: docker/setup-buildx-action@v3
 
       - name: Log in to GitHub Container Registry
-        uses: docker/login-action@v3
+        uses: docker/login-action@v4
         with:
           registry: ghcr.io
           username: ${{ github.actor }}