fix(helm): update chart loki-stack to 2.8.7

| datasource | package    | from  | to    |
| ---------- | ---------- | ----- | ----- |
| helm       | loki-stack | 2.8.4 | 2.8.7 |

Signed-off-by: Jarvis Plus Bot <112913195+jarvis-plus-bot[bot]@users.noreply.github.com>

k8s/namespaces/base/observability/loki-stack/helmrelease.yaml

@@ -9,7 +9,7 @@ spec:
   chart:
     spec:
       chart: loki-stack
-      version: 2.8.4
+      version: 2.8.7
       sourceRef:
         kind: HelmRepository
         name: grafana-charts