Use last_activity_at attr when showing the update date in project listing

app/views/shared/projects/_project.html.haml

@@ -7,7 +7,7 @@
 - show_last_commit_as_description = false unless local_assigns[:show_last_commit_as_description] == true && project.commit
 - css_class += " no-description" if project.description.blank? && !show_last_commit_as_description
 - cache_key = project_list_cache_key(project)
-- updated_tooltip = time_ago_with_tooltip(project.updated_at)
+- updated_tooltip = time_ago_with_tooltip(project.last_activity_at)
 
 %li.project-row{ class: css_class }
   = cache(cache_key) do

spec/features/dashboard/projects_spec.rb

@@ -15,6 +15,15 @@ RSpec.describe 'Dashboard Projects', feature: true do
     expect(page).to have_content('awesome stuff')
   end
 
+  it 'shows the last_activity_at attribute as the update date' do
+    now = Time.now
+    project.update_column(:last_activity_at, now)
+
+    visit dashboard_projects_path
+
+    expect(page).to have_xpath("//time[@datetime='#{now.getutc.iso8601}']")
+  end
+
   context 'when on Starred projects tab' do
     it 'shows only starred projects' do
       user.toggle_star(project2)