Update Redis image version to 7.1

Apparently we need a <major>.<minor> for anything past 7, so the sample wasn't working at the moment. Tested and 7.1 works.

Author: raphaeltm

samples/django-celery/compose.yaml

@@ -70,7 +70,7 @@ services:
       retries: 5
 
   broker:
-    image: redis:7
+    image: redis:7.1
     x-defang-redis: true
     ports:
       - mode: host