Update grafana/grafana Docker tag to v11.6.8

Author: renovate[bot]

docker-compose.yml

@@ -39,7 +39,7 @@ services:
     restart: always
 
   grafana:
-    image: grafana/grafana:11.5.2@sha256:8b37a2f028f164ce7b9889e1765b9d6ee23fec80f871d156fbf436d6198d32b7
+    image: grafana/grafana:11.6.8@sha256:0b5c6e4c8b871860f30cdfee33ed85f3ef40b070e11cc479eebcc9a4427706c0
     volumes:
       - grafana:/var/lib/grafana
       - ./config/grafana/dashboards/:/etc/grafana/dashboards/