Fixed group milestones date pickers not working

Closes #31095

app/assets/javascripts/dispatcher.js

@@ -150,13 +150,13 @@ const ShortcutsBlob = require('./shortcuts_blob');
         case 'projects:milestones:new':
         case 'projects:milestones:edit':
         case 'projects:milestones:update':
+        case 'groups:milestones:new':
+        case 'groups:milestones:edit':
+        case 'groups:milestones:update':
           new ZenMode();
           new gl.DueDateSelectors();
           new gl.GLForm($('.milestone-form'));
           break;
-        case 'groups:milestones:new':
-          new ZenMode();
-          break;
         case 'projects:compare:show':
           new gl.Diff();
           break;

app/assets/javascripts/dropzone_input.js

@@ -38,6 +38,9 @@ window.DropzoneInput = (function() {
       "opacity": 0,
       "display": "none"
     });
+
+    if (!project_uploads_path) return;
+
     dropzone = form_dropzone.dropzone({
       url: project_uploads_path,
       dictDefaultMessage: "",

changelogs/unreleased/group-milestone-date-fields-fix.yml

+---
+title: Fixed group milestone date dropdowns not opening
+merge_request:
+author:

spec/features/groups/milestone_spec.rb

+require 'rails_helper'
+
+feature 'Group milestones', :feature, :js do
+  let(:group) { create(:group) }
+  let!(:project) { create(:project_empty_repo, group: group) }
+  let(:user) { create(:group_member, :master, user: create(:user), group: group ).user }
+
+  before do
+    Timecop.freeze
+
+    login_as(user)
+  end
+
+  after do
+    Timecop.return
+  end
+
+  context 'create a milestone' do
+    before do
+      visit new_group_milestone_path(group)
+    end
+
+    it 'creates milestone with start date' do
+      fill_in 'Title', with: 'testing'
+      find('#milestone_start_date').click
+
+      page.within(find('.pika-single')) do
+        click_button '1'
+      end
+
+      click_button 'Create milestone'
+
+      expect(find('.start_date')).to have_content(Date.today.at_beginning_of_month.strftime('%b %-d, %Y'))
+    end
+  end
+end