Update deprecated slot syntax in promote_milestone_modal.vue

https://gitlab.com/gitlab-org/gitlab/-/merge_requests/31980

app/assets/javascripts/pages/milestones/shared/components/promote_milestone_modal.vue

@@ -68,7 +68,7 @@ export default {
     footer-primary-button-variant="warning"
     @submit="onSubmit"
   >
-    <template slot="title">
+    <template #title>
       {{ title }}
     </template>
     <div>

changelogs/unreleased/update-deprecated-slot-syntax-in---assets-javascripts-pages-milestone-pro.yml

+---
+title: Update deprecated slot syntax in ./app/assets/javascripts/pages/milestones/shared/components/promote_milestone_modal.vue
+merge_request: 31980
+author: Gilang Gumilar
+type: other