Update postgres Docker tag to v18.4

Author: renovate[bot]

docker/docker-compose-prod.yml

@@ -2,7 +2,7 @@ name: harmonia
 
 services:
   postgres:
-    image: postgres:18.1
+    image: postgres:18.4
     env_file:
       - .env
     restart: unless-stopped

docker/docker-compose-test.yml

@@ -2,7 +2,7 @@ name: harmonia
 
 services:
   postgres:
-    image: postgres:18.1
+    image: postgres:18.4
     env_file:
       - .env
     restart: unless-stopped

docker/local-setup/docker-compose.yml

@@ -2,7 +2,7 @@ name: harmonia
 
 services:
   postgres:
-    image: postgres:18.1
+    image: postgres:18.4
     container_name: harmonia-postgres
     restart: unless-stopped
     environment: