Fix navbar + menu flashing on page load (#31281) (#31342)

Backport #31281 by silverwind

Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

web_src/js/components/DiffCommitSelector.vue

@@ -202,7 +202,7 @@ export default {
     >
       <svg-icon name="octicon-git-commit"/>
     </button>
-    <div class="menu left transition" id="diff-commit-selector-menu" :class="{visible: menuVisible}" v-show="menuVisible" v-cloak :aria-expanded="menuVisible ? 'true': 'false'">
+    <div class="left menu" id="diff-commit-selector-menu" :class="{visible: menuVisible}" v-show="menuVisible" v-cloak :aria-expanded="menuVisible ? 'true': 'false'">
       <div class="loading-indicator is-loading" v-if="isLoading"/>
       <div v-if="!isLoading" class="vertical item" id="diff-commit-list-show-all" role="menuitem" @keydown.enter="showAllChanges()" @click="showAllChanges()">
         <div class="gt-ellipsis">