[EE] Reduce diff with CE in spec/models/milestone_spec.rb

Signed-off-by: Rémy Coutable <remy@rymai.me>

ee/spec/models/milestone_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Milestone do
+  describe "Associations" do
+    it { is_expected.to have_many(:boards) }
+  end
+end

spec/models/milestone_spec.rb

@@ -42,8 +42,6 @@ describe Milestone do
 
   describe "Associations" do
     it { is_expected.to belong_to(:project) }
-
-    it { is_expected.to have_many(:boards) }
     it { is_expected.to have_many(:issues) }
   end