chore(deps): update postgres docker tag to v18

compose.yml

@@ -2,7 +2,7 @@ version: "3.8"
 
 services: 
   db:
-    image: postgres:12.3
+    image: postgres:18.4
     deploy:
       labels:
         backupbot.backup: "${ENABLE_BACKUPS:-true}"

renovate.json

@@ -2,13 +2,5 @@
   "$schema": "https://docs.renovatebot.com/renovate-schema.json",
   "extends": [
     "config:recommended"
-  ],
-  "packageRules": [
-    {
-      "matchDatasources": [
-        "docker"
-      ],
-      "pinDigests": true
-    }
   ]
 }