Make sure to select `vertex-persistent` when looking for siblings (closes #3824)
Make sure to select `vertex-persistent` when looking for siblings
(closes #3824)

When hovering, there is also a companion `vertex-hover` element that might
sometimes get selected, and doesn't have the sibling class that enables drag.

bagage/iD,kartta-labs/iD,kartta-labs/iD,openstreetmap/iD,AndreasHae/iD,ngageoint/hootenanny-ui,openstreetmap/iD,1ec5/iD,ngageoint/hootenanny-ui,digidem/iD,AndreasHae/iD,edpop/iD,mapmeld/iD,mapmeld/iD,mapmeld/iD,ngageoint/hootenanny-ui,morray/iD,1ec5/iD,1ec5/iD,kartta-labs/iD,bagage/iD,edpop/iD,digidem/iD,AndreasHae/iD,edpop/iD,openstreetmap/iD,bagage/iD,morray/iD