chore(deps): update postgres docker tag to v18

Author: renovate[bot]

docker/docker-compose.yml

@@ -1,7 +1,7 @@
 services:
   # PostgreSQL Database
   postgres:
-    image: postgres:16-alpine
+    image: postgres:18-alpine
     container_name: renovate-dashboard-db
     restart: unless-stopped
     environment:

helm/renovate-dashboard/values.yaml

@@ -213,7 +213,7 @@ postgresql:
 
   image:
     repository: postgres
-    tag: "16-alpine"
+    tag: "18-alpine"
     pullPolicy: IfNotPresent
 
   # PostgreSQL credentials