chore(deps): update redis docker tag to v20.13.3 (#56)

This PR contains the following updates:

| Package | Update | Change |
|---|---|---|
| [redis](https://redirect.github.com/bitnami/charts)
([source](https://redirect.github.com/bitnami/charts/tree/HEAD/bitnami/redis))
| patch | `20.13.2` -> `20.13.3` |

---

### Release Notes

<details>
<summary>bitnami/charts (redis)</summary>

###
[`v20.13.3`](https://redirect.github.com/bitnami/charts/blob/HEAD/bitnami/redis/CHANGELOG.md#20133-2025-04-28)

- \[bitnami/redis] Release 20.13.3
([#&#8203;33217](https://redirect.github.com/bitnami/charts/pull/33217))

</details>

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charts/docker-mailserver/Chart.yaml

@@ -20,7 +20,7 @@ maintainers:
 - name: jeboehm
 dependencies:
 - name: redis
-  version: 20.13.2
+  version: 20.13.3
   repository: oci://registry-1.docker.io/bitnamicharts
   condition: redis.enabled
 - name: mariadb