chore(helm): update image docker.io/bitnami/alertmanager digest to 3debfa7 (#28269)

This PR contains the following updates:

| Package | Update | Change |
|---|---|---|
|
[docker.io/bitnami/alertmanager](https://redirect.github.com/bitnami/containers)
([source](https://redirect.github.com/bitnami/containers/tree/HEAD/bitnami/alertmanager))
| digest | `c71103f` -> `3debfa7` |

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charts/premium/prometheus/Chart.yaml

@@ -42,4 +42,4 @@ sources:
   - https://hub.docker.com/r/bitnami/prometheus
   - https://quay.io/thanos/thanos
 type: application
-version: 19.25.0
+version: 19.25.1

charts/premium/prometheus/values.yaml

@@ -6,7 +6,7 @@ thanosImage:
   tag: v0.36.1@sha256:e542959e1b36d5046083d1b64a7049c356b68a44a173c58b3ae7c0c9ada932d5
 alertmanagerImage:
   repository: docker.io/bitnami/alertmanager
-  tag: 0.27.0@sha256:c71103f194c0c953a0df492ae869663c3874d1b84a053ae62f8d503bf0b27a8f
+  tag: 0.27.0@sha256:3debfa7e4147bbb26c33b73b69bcc6a3ae093c47d6cd4a363e37ab7492260dba
 global:
   labels: {}
 workload: