Update docker.io/postgres Docker tag to v18

This PR contains the following updates:

| Package | Update | Change |
|---|---|---|
| [ghcr.io/kiwix/kiwix-serve](https://github.com/openzim/kiwix-tools) | minor | `3.7.0` -> `3.8.0` |

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### Configuration

📅 **Schedule**: Branch creation - At any time (no schedule defined), Automerge - At any time (no schedule defined).

🚦 **Automerge**: Disabled by config. Please merge this manually once you are satisfied.

♻ **Rebasing**: Whenever PR is behind base branch, or you tick the rebase/retry checkbox.

🔕 **Ignore**: Close this PR and you won't be reminded about this update again.

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 - [ ] <!-- rebase-check -->If you want to rebase/retry this PR, check this box

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This PR has been generated by [Renovate Bot](https://github.com/renovatebot/renovate).
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Reviewed-on: #1915
Co-authored-by: Renovate Bot <renovate-bot@alexlebens.net>
Co-committed-by: Renovate Bot <renovate-bot@alexlebens.net>

clusters/cl01tl/applications/kiwix/values.yaml

@@ -9,7 +9,7 @@ kiwix:
         main:
           image:
             repository: ghcr.io/kiwix/kiwix-serve
-            tag: 3.7.0
+            tag: 3.8.0
             pullPolicy: IfNotPresent
           args:
             - '*.zim'

hosts/ps10rp/gitea/compose.yaml

@@ -19,7 +19,7 @@ services:
             - /dev/net/tun:/dev/net/tun
 
     postgresql:
-        image: docker.io/postgres:17.6-alpine3.21
+        image: docker.io/postgres:18.0-alpine3.21
         container_name: gitea-postgres
         env_file:
             - .env