chore(deps): update docker.io/grafana/grafana docker tag to v11.6.8

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

Author: renovate[bot]

gitops/argocd/charts/observability/grafana-operator/values.yaml

@@ -8,7 +8,7 @@ ingress:
 grafanaOperator:
   instance:
     name: core
-    image: docker.io/grafana/grafana:11.6.0
+    image: docker.io/grafana/grafana:11.6.8
     installPlugins: "grafana-piechart-panel, grafana-lokiexplore-app, grafana-pyroscope-app, quickwit-quickwit-datasource"
     unsignedPlugins: "grafana-lokiexplore-app, grafana-pyroscope-app, quickwit-quickwit-datasource"
   matchLabels: