move tracing to 1.21 milestone

Author: dashpole

keps/prod-readiness/sig-instrumentation/647.yaml

@@ -0,0 +1,3 @@
+kep-number: 647
+alpha:
+  approver: "@wojtek-t"

keps/sig-instrumentation/647-apiserver-tracing/kep.yaml

@@ -23,9 +23,9 @@ see-also:
 replaces:
 stage: alpha
 last-updated: 2020-10-14
-latest-milestone: "v1.20"
+latest-milestone: "v1.21"
 milestone:
-  alpha: "v1.20"
+  alpha: "v1.21"
 feature-gates:
   - name: APIServerTracing
 disable-supported: true