Update docker.io/postgres Docker tag to v18

This PR contains the following updates:

| Package | Type | Update | Change |
|---|---|---|---|
| [actions/checkout](https://github.com/actions/checkout) | action | major | `v5` -> `v6` |

---

### Release Notes

<details>
<summary>actions/checkout (actions/checkout)</summary>

### [`v6`](https://github.com/actions/checkout/compare/v5...v6)

[Compare Source](https://github.com/actions/checkout/compare/v5...v6)

</details>

---

### 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.

---

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

---

This PR has been generated by [Renovate Bot](https://github.com/renovatebot/renovate).
<!--renovate-debug:eyJjcmVhdGVkSW5WZXIiOiI0Mi41LjAiLCJ1cGRhdGVkSW5WZXIiOiI0Mi41LjAiLCJ0YXJnZXRCcmFuY2giOiJtYWluIiwibGFiZWxzIjpbXX0=-->

Reviewed-on: #2064
Co-authored-by: Renovate Bot <renovate-bot@alexlebens.net>
Co-committed-by: Renovate Bot <renovate-bot@alexlebens.net>

.gitea/workflows/lint-test-docker-pull.yaml

@@ -13,7 +13,7 @@ jobs:
     runs-on: ubuntu-js
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           fetch-depth: 0
 

.gitea/workflows/lint-test-docker-push.yaml

@@ -13,7 +13,7 @@ jobs:
     runs-on: ubuntu-js
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           fetch-depth: 0
 

.gitea/workflows/lint-test-helm-pull.yaml

@@ -13,7 +13,7 @@ jobs:
     runs-on: ubuntu-js
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           fetch-depth: 0
 

.gitea/workflows/lint-test-helm-push.yaml

@@ -13,7 +13,7 @@ jobs:
     runs-on: ubuntu-js
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           fetch-depth: 0
 

.gitea/workflows/renovate.yaml

@@ -16,7 +16,7 @@ jobs:
     container: ghcr.io/renovatebot/renovate:42
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Renovate
         run: renovate

hosts/ps10rp/gitea/compose.yaml

@@ -19,7 +19,7 @@ services:
             - /dev/net/tun:/dev/net/tun
 
     postgresql:
-        image: docker.io/postgres:17.7-alpine3.21
+        image: docker.io/postgres:18.1-alpine3.21
         container_name: gitea-postgres
         env_file:
             - .env