Update Helm release postgres-cluster to v6

This PR contains the following updates:

| Package | Update | Change |
|---|---|---|
| [loki](https://grafana.github.io/helm-charts) ([source](https://github.com/grafana/helm-charts)) | minor | `6.30.1` -> `6.31.0` |

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### 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.

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 - [ ] <!-- rebase-check -->If you want to rebase/retry this PR, check this box

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Reviewed-on: #880
Co-authored-by: Renovate Bot <renovate-bot@alexlebens.net>
Co-committed-by: Renovate Bot <renovate-bot@alexlebens.net>

clusters/cl01tl/monitoring/loki/Chart.yaml

@@ -16,7 +16,7 @@ maintainers:
   - name: alexlebens
 dependencies:
   - name: loki
-    version: 6.30.1
+    version: 6.31.0
     repository: https://grafana.github.io/helm-charts
   - name: promtail
     version: 6.17.0