Fix tooltip on pipelines page not updating

Fix @psimyn comment
https://gitlab.com/gitlab-org/gitlab-ce/issues/33194#note_31340102

app/assets/javascripts/pipelines/components/stage.vue

@@ -16,6 +16,7 @@
 /* global Flash */
 import { borderlessStatusIconEntityMap } from '../../vue_shared/ci_status_icons';
 import loadingIcon from '../../vue_shared/components/loading_icon.vue';
+import tooltipMixin from '../../vue_shared/mixins/tooltip';
 
 export default {
   props: {
@@ -31,6 +32,10 @@ export default {
     },
   },
 
+  mixins: [
+    tooltipMixin,
+  ],
+
   data() {
     return {
       isLoading: false,
@@ -127,9 +132,10 @@ export default {
 <template>
   <div class="dropdown">
     <button
+      ref="tooltip"
       :class="triggerButtonClass"
       @click="onClickStage"
-      class="mini-pipeline-graph-dropdown-toggle has-tooltip js-builds-dropdown-button"
+      class="mini-pipeline-graph-dropdown-toggle js-builds-dropdown-button"
       :title="stage.title"
       data-placement="top"
       data-toggle="dropdown"