Renovate: Update docker/build-push-action action to v7 (#576)

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
|
[docker/build-push-action](https://redirect.github.com/docker/build-push-action)
| action | major | `v6` → `v7` |

---

### Release Notes

<details>
<summary>docker/build-push-action (docker/build-push-action)</summary>

###
[`v7`](https://redirect.github.com/docker/build-push-action/compare/v6...v7)

[Compare
Source](https://redirect.github.com/docker/build-push-action/compare/v6...v7)

</details>

---

### Configuration

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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 was generated by [Mend Renovate](https://mend.io/renovate/).
View the [repository job
log](https://developer.mend.io/github/cobaltcore-dev/cortex).

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Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

.github/workflows/push-images.yaml

@@ -54,7 +54,7 @@ jobs:
       - name: Build and Push Cortex Postgres
         if: steps.changed_postgres_files.outputs.all_changed_files != ''
         id: push_cortex_postgres
-        uses: docker/build-push-action@v6
+        uses: docker/build-push-action@v7
         with:
           context: postgres
           platforms: linux/amd64,linux/arm64
@@ -87,7 +87,7 @@ jobs:
           DOCKER_METADATA_SHORT_SHA_LENGTH: 8
       - name: Build and Push Cortex
         id: push_cortex
-        uses: docker/build-push-action@v6
+        uses: docker/build-push-action@v7
         with:
           context: .
           file: Dockerfile