Update kep-3902's release target to 1.29

Author: yuanchen8911

keps/sig-scheduling/3902-decoupled-taint-manager/kep.yaml

@@ -31,11 +31,11 @@ stage: beta
 # The most recent milestone for which work toward delivery of this KEP has been
 # done. This can be the current (upcoming) milestone, if it is being actively
 # worked on.
-latest-milestone: "v1.28"
+latest-milestone: "v1.29"
 
 # The milestone at which this feature was, or is targeted to be, at each stage.
 milestone:
-  beta: "v1.28"
+  beta: "v1.29"
 
 # The following PRR answers are required at alpha release
 # List the feature gate name and the components for which it must be enabled