mark 3960 implemented

Author: AxeZhan

keps/sig-node/3960-pod-lifecycle-sleep-action/kep.yaml

@@ -4,7 +4,7 @@ authors:
   - "@AxeZhan"
 owning-sig: sig-node
 participating-sigs: []
-status: implementable
+status: implemented
 creation-date: 2023-04-22
 reviewers:
   - "@thockin"