Fix page layout for sidebar on designs view

The .layout-page div was missing the .right-sidebar-expanded class,
causing the main content to be misaligned.

app/helpers/nav_helper.rb

@@ -20,7 +20,6 @@ module NavHelper
 
   def page_gutter_class
     if page_has_markdown?
-
       if cookies[:collapsed_gutter] == 'true'
         %w[page-gutter right-sidebar-collapsed]
       else

ee/app/helpers/ee/nav_helper.rb

@@ -11,7 +11,9 @@ module EE
 
     override :page_has_markdown?
     def page_has_markdown?
-      super || current_path?('epics#show')
+      super ||
+        current_path?('epics#show') ||
+        current_path?('issues#designs')
     end
 
     override :admin_monitoring_nav_links

ee/changelogs/unreleased/fix-issues-designs-sidebar.yml

+---
+title: Fix page layout for sidebar on designs view
+merge_request: 17579
+author:
+type: fixed

ee/spec/features/projects/issues/design_management/user_views_designs_spec.rb

@@ -9,16 +9,28 @@ describe 'User views issue designs', :js do
   before do
     enable_design_management
 
-    create(:design, :with_file, issue: issue, filename: 'world.png')
-
-    visit project_issue_path(project, issue)
+    create(:design, :with_file, issue: issue)
+  end
 
-    click_link 'Designs'
+  context 'navigates from the issue view' do
+    before do
+      visit project_issue_path(project, issue)
+      click_link 'Designs'
+      wait_for_requests
+    end
 
-    wait_for_requests
+    it 'fetches list of designs' do
+      expect(page).to have_selector('.js-design-list-item', count: 1)
+    end
   end
 
-  it 'fetches list of designs' do
-    expect(page).to have_selector('.js-design-list-item', count: 1)
+  context 'navigates directly to the design view' do
+    before do
+      visit designs_project_issue_path(project, issue)
+    end
+
+    it 'expands the sidebar' do
+      expect(page).to have_selector('.layout-page.right-sidebar-expanded')
+    end
   end
 end