fix: remove named volume from volume prune example

The default docker volume prune only removes anonymous volumes, but
the example output included "my-named-vol" which is a named volume.
Removed it to match the documented behavior.

Fixes #24007

data/engine-cli/docker_volume_prune.yaml

@@ -60,7 +60,6 @@ examples: |-
     Are you sure you want to continue? [y/N] y
     Deleted Volumes:
     07c7bdf3e34ab76d921894c2b834f073721fccfbbcba792aa7648e3a7a664c2e
-    my-named-vol
 
     Total reclaimed space: 36 B
     ```