KEP-3619: updated 'stage' field in kep.yaml

Author: everpeace

keps/sig-node/3619-supplemental-groups-policy/kep.yaml

@@ -19,7 +19,7 @@ see-also: []
 replaces: []
 
 # The target maturity stage in the current dev cycle for this KEP.
-stage: alpha
+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