releng: Add 1.25 and remove 1.21 milestone_applier rules
releng: Add 1.25 and remove 1.21 milestone_applier rules

Signed-off-by: Jeremy Rickard <ce0adbd98e5d6a5af213bdf686db1ed8a5788b29@gmail.com>

jessfraz/test-infra,cblecker/test-infra,michelle192837/test-infra,kubernetes/test-infra,cjwagner/test-infra,jessfraz/test-infra,dims/test-infra,jessfraz/test-infra,michelle192837/test-infra,cjwagner/test-infra,cblecker/test-infra,dims/test-infra,kubernetes/test-infra,kubernetes/test-infra,cjwagner/test-infra,cjwagner/test-infra,michelle192837/test-infra,michelle192837/test-infra,kubernetes/test-infra,kubernetes/test-infra,michelle192837/test-infra,cblecker/test-infra,michelle192837/test-infra,BenTheElder/test-infra,jessfraz/test-infra,BenTheElder/test-infra,dims/test-infra,BenTheElder/test-infra,BenTheElder/test-infra,dims/test-infra,cjwagner/test-infra,cjwagner/test-infra,BenTheElder/test-infra,cblecker/test-infra,dims/test-infra,jessfraz/test-infra,cblecker/test-infra,dims/test-infra,jessfraz/test-infra,BenTheElder/test-infra,kubernetes/test-infra,cblecker/test-infra