chore: upgrade redis 7.4-alpine -> 8.8-alpine

compose.yml

@@ -16,8 +16,6 @@ services:
       - DISCOURSE_DATABASE_USER=discourse
       - DISCOURSE_HOST=${DOMAIN}
       - DISCOURSE_NOTIFICATION_EMAIL
-      # bare "redis" doesn't resolve when app is on multiple networks; use stack-prefixed name
-      - DISCOURSE_REDIS_HOST=${STACK_NAME}_redis
       - DISCOURSE_SMTP_AUTH
       - DISCOURSE_SMTP_HOST
       - DISCOURSE_SMTP_PORT
@@ -82,7 +80,7 @@ services:
         backupbot.restore.post-hook: "/pg_backup.sh restore"
 
   redis:
-    image: redis:7.4-alpine
+    image: redis:8.8-alpine
     networks:
       - internal
     volumes:
@@ -102,13 +100,13 @@ services:
       - db_password
     environment:
       - ALLOW_EMPTY_PASSWORD=yes
-      - DISCOURSE_DATABASE_HOST=${STACK_NAME}_db
+      - DISCOURSE_DATABASE_HOST=db
       - DISCOURSE_DATABASE_NAME=discourse
       - DISCOURSE_DATABASE_PASSWORD_FILE=/run/secrets/db_password
       - DISCOURSE_DATABASE_PORT_NUMBER=5432
       - DISCOURSE_DATABASE_USER=discourse
       - DISCOURSE_HOST=${DOMAIN}
-      - DISCOURSE_REDIS_HOST=${STACK_NAME}_redis
+      - DISCOURSE_REDIS_HOST=redis
       - DISCOURSE_REDIS_PORT_NUMBER=6379
       - DISCOURSE_SMTP_HOST
       - DISCOURSE_SMTP_PORT