Update MR based on Sean's feedback

app/controllers/dashboard/milestones_controller.rb

@@ -10,7 +10,7 @@ class Dashboard::MilestonesController < Dashboard::ApplicationController
   def index
     respond_to do |format|
       format.html do
-        @milestone_states = Milestone.states_count(@projects, @groups)
+        @milestone_states = Milestone.states_count(@projects.select(:id), @groups.select(:id))
         @milestones = Kaminari.paginate_array(milestones).page(params[:page])
       end
       format.json do

changelogs/unreleased/rz_fix_milestone_count.yml

 ---
 title: Fixing count on Milestones
 merge_request: 21446
-author: eagllus
+author:
 type: fixed

spec/models/milestone_spec.rb

@@ -351,12 +351,12 @@ describe Milestone do
 
   describe '.states_count' do
     context 'when the projects have milestones' do
-      let(:project_1) { create(:project) }
-      let(:project_2) { create(:project) }
-      let(:group_1) { create(:group) }
-      let(:group_2) { create(:group) }
-
       before do
+        project_1 = create(:project)
+        project_2 = create(:project)
+        group_1 = create(:group)
+        group_2 = create(:group)
+
         create(:active_milestone, title: 'Active Group Milestone', project: project_1)
         create(:closed_milestone, title: 'Closed Group Milestone', project: project_1)
         create(:active_milestone, title: 'Active Group Milestone', project: project_2)