KEP-4601: update stage to stable for 1.34

Author: liggitt

keps/sig-auth/4601-authorize-with-selectors/kep.yaml

@@ -16,7 +16,7 @@ see-also:
 replaces:
 
 # The target maturity stage in the current dev cycle for this KEP.
-stage: beta
+stage: stable
 
 # 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