Fix invalid milestone URL for new milestone dropdown

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/views/dashboard/milestones/index.html.haml

@@ -8,7 +8,7 @@
   - if current_user
     .page-title-controls
       = render 'shared/new_project_item_select',
-        path: 'milestones/new', label: 'New milestone',
+        path: '-/milestones/new', label: 'New milestone',
         include_groups: true, type: :milestones
 
 .top-area

changelogs/unreleased/64321-wrong-url-when-creating-milestones-from-instance-milestones-dashboard.yml

+---
+title: Fix wrong URL when creating milestones from instance milestones dashboard
+merge_request: 30512
+author:
+type: fixed

spec/features/dashboard/milestones_spec.rb

@@ -29,5 +29,19 @@ describe 'Dashboard > Milestones' do
       expect(page).to have_content(milestone.title)
       expect(page).to have_content(group.name)
     end
+
+    describe 'new milestones dropdown', :js do
+      it 'takes user to a new milestone page', :js do
+        find('.new-project-item-select-button').click
+
+        page.within('.select2-results') do
+          first('.select2-result-label').click
+        end
+
+        find('.new-project-item-link').click
+
+        expect(current_path).to eq(new_group_milestone_path(group))
+      end
+    end
   end
 end