Changes the conditional render of the tree component on diffs

Closes https://gitlab.com/gitlab-org/gitlab/-/issues/223086

app/assets/javascripts/diffs/components/app.vue

@@ -398,7 +398,7 @@ export default {
         class="files d-flex"
       >
         <div
-          v-show="showTreeList"
+          v-if="showTreeList"
           :style="{ width: `${treeWidth}px` }"
           class="diff-tree-list js-diff-tree-list mr-3"
         >