KEP-3998: Update feature status

Signed-off-by: Yuki Iwai <[email protected]>

Author: tenzen-y

keps/sig-apps/3998-job-success-completion-policy/kep.yaml

@@ -5,7 +5,7 @@ authors:
 owning-sig: sig-apps
 participating-sigs:
   - sig-apps
-status: implementable
+status: implemented
 creation-date: 2023-06-05
 reviewers:
   - "@mimowo"