Update Helm release grafana-loki to v4.8.15

Author: renovate[bot]

charts/nopo11y-stack/Chart.yaml

@@ -12,7 +12,7 @@ dependencies:
 - condition: grafana-loki.enabled
   name: grafana-loki
   repository: https://charts.bitnami.com/bitnami
-  version: 4.6.18
+  version: 4.8.15
 - condition: promtail.enabled
   name: promtail
   repository: https://grafana.github.io/helm-charts