chore(helm): update image public.ecr.aws/bitnami/alertmanager digest to 5941159 (#31949)

This PR contains the following updates:

| Package | Update | Change |
|---|---|---|
|
[public.ecr.aws/bitnami/alertmanager](https://redirect.github.com/bitnami/containers)
([source](https://redirect.github.com/bitnami/containers/tree/HEAD/bitnami/alertmanager))
| digest | `a28f966` -> `5941159` |

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charts/premium/prometheus/Chart.yaml

@@ -42,4 +42,4 @@ sources:
   - https://github.com/truecharts/charts/tree/master/charts/premium/prometheus
   - https://quay.io/thanos/thanos
 type: application
-version: 21.3.1
+version: 21.3.2

charts/premium/prometheus/values.yaml

@@ -6,7 +6,7 @@ thanosImage:
   tag: v0.37.2@sha256:4ec6df40fdb921de162677b321057caa8fb8324c65f4cfae9568ed55c4469e2c
 alertmanagerImage:
   repository: public.ecr.aws/bitnami/alertmanager
-  tag: 0.28.0@sha256:a28f966e3eb374778401554699fc4001f0635d30825f24ef2cc772dd2766ea52
+  tag: 0.28.0@sha256:594115949097238b9ca59615a4880da65832f8beef79b6b7061506d9ff5090b5
 global:
   labels: {}
 workload: