fix(components): [collapse] fix triggering form action when inside it (#14308)

When el-collapse with el-collapse-item is placed inside a form and the collapse trigger btn is
pressed, form's action as triggered. This fixes it

closed #14304

packages/components/collapse/src/collapse-item.vue

@@ -7,6 +7,7 @@
       :aria-controls="scopedContentId"
       :aria-describedby="scopedContentId"
       :tabindex="disabled ? -1 : 0"
+      type="button"
       @click="handleHeaderClick"
       @keydown.space.enter.stop.prevent="handleEnterClick"
       @focus="handleFocus"