fix(transition): transition-group should only listen for first-level children's end events (#8374)

Author: verstoff

src/platforms/web/runtime/components/transition-group.js

@@ -116,6 +116,9 @@ export default {
         addTransitionClass(el, moveClass)
         s.transform = s.WebkitTransform = s.transitionDuration = ''
         el.addEventListener(transitionEndEvent, el._moveCb = function cb (e) {
+          if (e && e.target !== el) {
+            return
+          }
           if (!e || /transform$/.test(e.propertyName)) {
             el.removeEventListener(transitionEndEvent, cb)
             el._moveCb = null