Pin Postgres image version in docker-compose examples to avoid unexpected upgrades

contrib/docker-compose/basic.yml

@@ -19,7 +19,7 @@ services:
     # healthcheck:
     #  test: ["CMD", "/usr/bin/miniflux", "-healthcheck", "auto"]
   db:
-    image: postgres:latest
+    image: postgres:15
     container_name: postgres
     environment:
       - POSTGRES_USER=miniflux

contrib/docker-compose/caddy.yml

@@ -25,7 +25,7 @@ services:
       - ADMIN_PASSWORD=test123
       - BASE_URL=https://miniflux.example.org
   db:
-    image: postgres:latest
+    image: postgres:15
     container_name: postgres
     environment:
       - POSTGRES_USER=miniflux

contrib/docker-compose/traefik.yml

@@ -37,7 +37,7 @@ services:
       - "traefik.http.routers.miniflux.entrypoints=websecure"
       - "traefik.http.routers.miniflux.tls.certresolver=myresolver"
   db:
-    image: postgres:latest
+    image: postgres:15
     container_name: postgres
     environment:
       - POSTGRES_USER=miniflux