Make UnitGroup trigger sort on UNIT_PET

src/types/unitgroup.lua

@@ -84,6 +84,7 @@ function UnitGroup:RegisterEvents()
     frame:RegisterEvent("GROUP_ROSTER_UPDATE")
     frame:RegisterEvent("PLAYER_REGEN_ENABLED")
     frame:RegisterEvent("PLAYER_ENTERING_WORLD")
+    frame:RegisterEvent("UNIT_PET")
 end
 
 function UnitGroup:GROUP_ROSTER_UPDATE()
@@ -94,6 +95,10 @@ function UnitGroup:PLAYER_ENTERING_WORLD()
     self:OnRosterUpdate()
 end
 
+function UnitGroup:UNIT_PET()
+    self:OnRosterUpdate()
+end
+
 function UnitGroup:PLAYER_REGEN_ENABLED()
     self:OnLeaveCombat()
 end