Update Helm release promtail to v6.15.5 (#117)

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

Author: renovate[bot]

manifests/_apps/logging.yaml

@@ -63,7 +63,7 @@ spec:
   source:
     chart: promtail
     repoURL: https://grafana.github.io/helm-charts
-    targetRevision: 6.15.4
+    targetRevision: 6.15.5
     helm:
       values: |-
         serviceMonitor: