bump the prod-readiness file

Author: Han Kang

keps/prod-readiness/sig-instrumentation/1209.yaml

@@ -1,3 +1,3 @@
 kep-number: 1209
-beta:
+stable:
   approver: "@johnbelamaric"

keps/sig-instrumentation/1209-metrics-stability/kep.yaml

@@ -25,10 +25,10 @@ reviewers:
   - "@sttts" # api-machinery
   - "@bsalamat" # scheduling
   - "@andrewsykim" # cloud-provider
-  - "@johnbelamaric" # PRR-reviewer
 approvers:
   - "@brancz"
 prr-approvers:
+  - "@johnbelamaric" # PRR-reviewer
 see-also:
   - "/keps/sig-instrumentation/1206-metrics-overhaul"