chore(deps): update postgres docker tag to v18.3

Author: renovate[bot]

spring-keycloak-example/compose.yaml

@@ -57,7 +57,7 @@ services:
       - spring_keycloak
 
   keycloak-database:
-    image: postgres:18.2-alpine3.22
+    image: postgres:18.3-alpine3.22
     container_name: keycloak-database
     environment:
       POSTGRES_USER: postgres #⚠️ DO NOT USE IN PRODUCTION