kep-4832: promote to beta

Author: sanposhiho

keps/sig-scheduling/4832-async-preemption/kep.yaml

@@ -20,6 +20,7 @@ latest-milestone: "v1.32"
 # The milestone at which this feature was, or is targeted to be, at each stage.
 milestone:
   alpha: "v1.32"
+  beta: "v1.33"
 
 # The following PRR answers are required at alpha release
 # List the feature gate name and the components for which it must be enabled