fix: snok/container-retention-policy cut-off param default after new …

…major release (#94)

.github/workflows/clean-ghcr.yaml

@@ -5,7 +5,7 @@ on:
     inputs:
       cut-off:
         type: string
-        default: A week ago UTC
+        default: 7days
         description: The timezone-aware datetime you want to delete container versions that are older than.
 
 permissions: {}